LI 


1  )EPARTMENT  <  >1     \< !  I  Tl  fRE, 

BUREAU   01 

L    O   M 


WHITE  FLIES  INJURIOUS  TO  CITRUS 

IN  FLORIDA. 


BY 


A.  W.  MORRILL,  Ph.  D. 

AND 

E.  A.  BACK,  Ph.  D. 


July  12,  li»n. 


omaMH&r 


U.S.  DEPOSITORY 


fflNGTON: 
GOVK  PRINTING   OFFICE. 


\ 


Bui.  92,  Bureau  of   Entomology,  U.  S.  Dept.  of  Agriculture. 


Plate  I. 


Fig  1  .—Orange  Covered  with  Sooty  Mold. 


Fig.  2.— Leaf  of  Orange  Coated  with  Sooty  Mold. 


U.  s.  DEPAR  IMIA  r  OF   AGRICULTURE, 

BUREAU   OF   ENTOMOLOGY     BULLETIN  N<>.  92. 

L.  O.  I  H  >WARD.  Kntomologilt  and  <   Inrf  ■  >!  Burrau. 


w 


CE  FLIES   INJURIOUS  TO  CITRUS 
IX  FLORIDA. 


A.  W.  MORRILL,  Ph.  D., 

AND 

E.  A.  BACK,  Ph.  D. 


Issued  July  12,  1911. 


WASHINGTON: 

GOVERNMENT    PRINTING    OFFICE. 

1911. 


BUREAU  OF  ENTOMOLOGY. 

L.  0.  Howard,  Entomologist  and  Chief  of  Bureau. 
C.  L.  Marlatt,  Entomologist  and  Acting  Chief  in  Absence  of  Chief. 
R.  S.  Clifton,  Executive  Assistant. 
W.  F.  Tastet,  Chief  Clerk. 
F.  H.  Chittenden,  in  charge  of  truck  crop  and  stored  product  insect  investigations. 
A.  D.  Hopkins,  in  charge  of  forest  insect  investigations. 
W.  D.  Hunter,  in  charge  of  southern  field  crop  insect  investigations. 
F.  M.  Webster,  in  charge  of  cereal  and  forage  insect  investigations. 
A.  L.  Quaintance,  in  charge  of  deciduous  fruit  insect  investigations. 
E.  F.  Phillips,  in  charge  of  bee  culture. 

D.  M.  Rogers,  in  charge  of  preventing  spread  of  moths,  field  work. 
Rolla  P.  Currie,  in  charge  of  editorial  work. 
Mabel  Colcord,  librarian. 


LETTER  Or  TRANSMITTAL 


United  States  Department  of  Agriculture, 

Bureau  of  Entomology, 

Washington,  D.  C,  March  2,  1911 . 

Sm:  I  have4  the  honor  to  transmit  herewith,  for  publication  as 
Bulletin  92  of  the  Bureau  of  Entomology,  a  manuscript  prepared  by 
Drs.  A.  W.  Morrill  and  E.  A.  Back,  dealing  with  the  life  history  of 
the  white  flies  injurious  to  citrus  trees  in  Florida. 

The  investigation  of  the  citrus  white  flies  in  Florida,  under  the 
genera]  direction  of  the  assistant  chief  of  this  bureau,  Mr.  C.  L.  Marlatt, 
was  begun  in  1906,  and  is  now  approaching  completion.  There  has 
already  been  published  a  bulletin  (No.  76)  dealing  fully  with  the 
general  subject  of  fumigation  with  hydrocyanic-acid  gas  for  the  white 
fly.  A  circular  (No.  Ill)  has  also  been  issued,  giving  brief  directions 
for  winter  fumigation. 

The  present  publication  is  a  general  account  of  the-  two  species  of 
white  flies  which  are  of  special  economic  importance  to  the  citrus 
grower  in  Florida.  The  publication  includes  the  history  of  these 
insects  in  the  United  States,  their  distribution  and  food  plants,  and 
a  very  detailed  study  of  the  habits  and  life  cycle  of  the  two  species. 
A  great  deal  of  painstaking  and  minute  work  has  been  done,  and  the 
information  secured  furnishes  an  accurate  foundation  for  the  develop- 
ing of  the  best  means  of  control. 

Supplementing  this  publication,  which  deals  largely  with  life  his- 
tory and  habits,  it  is  proposed  to  publish  a  bulletin  on  control  by 
sprays,  fungi,  and  other  enemies,  and  to  supplement  or  reissue  in 
revised  form  the  bulletin  dealing  with  fumigation. 
Respectfully, 

L.  O.  Howard, 

Entomologist  and  Chief  of  Bureau. 
Hon.  James  Wilson, 

Secretary  of  Agriculture. 

3 


CO  NTH  NTS. 


Introduction 9 

Species  of  white  flies  affecting  citrus LO 

The  citrus  white  fly  (Aleyrodea  citri  II.  and  II.) II 

Bistorical  review 11 

Origin 11 

Early  history  in  the  United  States 12 

Literature 14 

Injury 17 

Nature  of  injury. 17 

Loss  of  sap 17 

Sooty  mold 17 

Extent  of  injury 19 

Injury  to  fruit 19 

Injury  to  trees 23 

Summary  of  losses 23 

Increased  cost  of  maintenance 24 

Distribution 25 

In  the  United  States ' 25 

In  foreign  countries 27 

Food  plants 28 

Authentic  and  questionable  records 28 

Economic  significance  of  food  plants  and  interrelationship  between 

food  plants  and  insects 31 

<  itrus 32 

China  trees  and  umbrella  trees 34 

( la  pe  Jessamine 39 

Privet  hedges 40 

Japanese  and  wild  persimmons 41 

Lilac 42 

Prickly  ash 42 

Coffee 43 

Occasionally  infested  food  plants 43 

Spread  in  the  United  States 43 

(  hecks  on  successful  establishment 43 

Flight  of  adults 44 

Winds 48 

Vehicles,  railroad  trains,  and  boats 48 

Citrus  nursery  stock  and  ornamental  plants 49 

Accidental  spread  by  man 50 

Life  history  and  habits 51 

Summary 51 

Methods  of  study 52 

The  egg 53 

Description 53 

Duration  of  egg  stage 54 

5 


6  WHITE   FLIES   INJURIOUS   TO    CITRUS   IN    FLORIDA. 

The  citrus  white  fly— Continued.  Page. 
Life  history  and  habits — Continued. 
The  egg — Continued. 

Parthenogenesis 57 

Hatching 57 

The  larval  and  pupal  stages 58 

Description  of  stages : 58 

Duration  of  stages 62 

Locomotion 63 

Growth 64 

Molts 64 

Feeding  habits  of  larvae  and  pupa? 65 

The  adult 65 

Description 66 

Emergence 67 

Duration  of  life 71 

Mating 71 

Oviposition 72 

Proportion  of  sexes 77 

Influence  of  weather  conditions  on  activity  of  adults 78 

Feeding  habits  of  adults 78 

Multiplication 79 

Length  of  life  cycle 80 

Seasonal  history 81 

Generations  of  the  citrus  white  fly 81 

Seasonal  fluctuations  in  the  numbers  of  adults  or  so-called  "broods"..  84 

The  cloudy- winged  white  fly  (Aleyrodes  nubifera  Berger) 86 

History 86 

Amount  of  injury  by  the  cloudy- winged  white  fly 87 

Distribution 89 

Food  plants 90 

Spread 90 

Life  history  and  habits 91 

The  egg 91 

The  larval  and  pupal  stages '. 94 

The  adult 98 

Length  of  life  cycle 100 

Seasonal  history 101 

Generations  of  the  cloudy- winged  white  fly 101 

Seasonal  fluctuations  in  numbers  of  adults  or  so-called  "broods  " 102 

Index 105 


ILLUSTRATIONS. 


PI  |  ii  B 

Page. 
Plats  I.  Pig.  l.    Orange  covered  with  Booty  mold.     Fig.  2.     Leal  of  orange 

coated    with    sooty    Illold I'Yont  i.-|  >i<-<  ... 

II.  Fig.  l.  -Aleyrodes  wort  on  mulberry.  Fig.  2. — Woolly  white  fly 
(Aleyrodes  houxtrdi)  on  orange.  Fig.  3.  Paraleyrodes  persese  on 
orange.  Fig.  4. — Woolly  white  fly  (Aleyrodes  howardi)  showing 
eggs  in  circles,  and  adults,     tig.  5. — Aleyrodes  sp.  on  sea  grape.  . .         10 

III.  Fig.  1 . — Sooty  mold  on  orange  following  white-fly  attack ;  broken  and 

falling  from  leaf.     Fig.  2. — Sooty  mold  on  cinnamon  tree  following 
attacks  by  cinnamon  scale 18 

IV.  Fig.  1. — China  tree  defoliated  during  winter.     Fig.  2. — Same  tree  in 

full  foliage  in  summer 34 

Y.  Fig.  1. — Leaflet  of  umbrella  China  tree  showing  infestation  by  A. 
ritri.     Fig.  2. — Umbrella  China  tree  infested  by  A.  citri,  showing 

orange  trees  in  rear  of  house 34 

VI.  Fig.  1. — Nursery  citrus  trees  infested  with  white  flies,  set  out  in  an 
isolated  noninfested  grove  without  having  leaves  removed.  Fig. 
2. — Buggy  in  an  orange  grove;  buggy-top  full  of  adult  white  flies 
ready  to  be  carried  to  other  groves.  Fig.  3. — Train  at  station ;  adult 
citrus  white  flies  swarming  from  near-by  umbrella  China  tree  into 
coaches  ready  to  be  carried  for  miles  down  the  Florida  east  coast. .  48 
VII.  Fig.  1. — Rearing  cages  in  position  on  orange  trees.  Fig.  2. — En- 
larged rearing  cage 52 

VIII.  Fig.  1. — Leaf  showing  pupa  cases  of  A.  citri;  also  pupae  and  eggs. 
Fig.  2. — Leaf  showing  heavy  infestation  by  A.  citri.     Fig.  3. — 

Leaf  showing  pupa  cases  of  A.  nubifera 62 

IX.  Fig.  1. — Tender  shoot  swarming  with  adult  citrus  white  flies.     Fig. 

2. — Leaf  of  same,  enlarged 66 

X.  Fig.  1. — Adults  of  A.  nubifera,  the  cloudy-winged  white  fly,  and 
many  eggs  scattered  over  leaf.  Fig.  2. — Larva?  and  pupae  of  both 
the  citrus  white  fly  and  cloudy-winged  white  fly  killed  by  fumi- 
gation, and  eggs  of  the  citrus  white  fly  along  midrib 98 

TEXT   FIGURES. 

Fig.    1.  Map  showing  distribution  of  the  citrus  white  fly  (Aleyrodes  citri)  in 

Florida 26 

2.  Diagram  of  laboratory  grounds  at  Orlando,  Fla 37 

3.  The  citrus  white  fly:  Eggs 53 

4.  The  citrus  white  fly:  Larva,  first  instar,  dorsal  view 59 

5.  The  citrus  white  fly:  Larva,  first  instar,  ventral  view 59 

6.  The  citrus  white  fly:  Antenna  and  left  hind  leg;  first  instar  larva 59 

7.  The  citrus  white  fly:  Larva,  second  instar,  ventral  view 60 

8.  The  citrus  white  fly :  Larva,  third  instar,  ventral  view 60 

7 


8  WHITE   FLIES   INJURIOUS   TO    CITRUS  IN   FLORIDA. 

Page. 

Fig.    9.  The  citrus  white  fly:  Pupa  and  details 61 

10.  The  citrus  white  fly:  Adult  and  details 66 

11.  Diagram  showing  annual  generations  of  the  citrus  white  fly 82 

12.  Diagram  showing  abundance  of  adults  of  the  citrus  white  fly  at  Or- 

lando, Fla.,  throughout  1909 84 

13.  Map  showing  distribution  of  the  cloudy-winged  white  fly  {Aleyrodes 

nubifera)  in  Florida 90 

14.  The  cloudy-winged  white  fly :  Eggs 91 

15.  The  cloudy-winged  white  fly:  Larva,  first  instar,  ventral  view 94 

16.  The  cloudy-winged  white  fly:  Larva,  third  instar,  ventral  view 95 

17.  The  cloudy- winged  white  fly:  Pupa  and  details 95 

18.  The  cloudy-winged  white  fly:  Dorsal  view  of  pupa,  showing  adult 

insects  about  to  emerge 95 

19.  Diagram  showing  relative  abundance  of  adults  of  the  cloudy-winged 

white  fly  and  the  citrus  white  fly,  throughout  1909.  at  Orlando  Fla . .  103 


WHITL  FLIES  INJURIOUS  TO  CITRUS  IN  FLORIDA. 


INTRODUCTION. 

The  present  bulletin  includes  the  principal  results  of  studies  of  the 
two  species  of  white  (lies  most  destructive  to  Citrus  in  the  United 
States,  commonly  known  as  the  citrus  white  fly  {Aleyrodes  citri  K. 
&  II.)  and  the  cloudy-winged  white  fly  (Aleyrodes  nubifera  Berger). 
With  these  pests  successful  control  measures  must  be  based  on  a 
complete  understanding  of  the  insects  themselves.  On  this  account 
the  study  of  the  insects,  their  life  history,  seasonal  history,  habits, 
food-plant  relationships,  and  related  topics  has  occupied  an  unusually 
important  position  in  the  white-fly  investigations. 

The  authors  have  concluded  that  unless  natural  enemies  capable 
of  controlling  the  two  white-fly  pests  are  existent  and  are  secured, 
control  measures  will  require  permanent  expert  supervision  for  the 
most  satisfactory  and  economical  results — not  supervision  of  work  in 
individual  citrus  groves,  but  supervision  aimed  principally  to  prop- 
erly correlate  individual  efforts  and  to  take  full  advantage  of  favoring 
local  conditions.  For  supervision  of  this  nature,  a  good  foundation 
of  extensive  and  reliable  studies  of  the  insects  is  necessary.  While 
the  portion  of  the  white-fly  investigations  herein  reported  is  com- 
paratively extensive,  it  is  necessarily  not  exhaustive  and  in  the 
course  of  time  certain  features  of  this  work  can  undoubtedly  be  con- 
tinued with  profit  as  an  aid  to  the  future  improvement  of  control 
measures. 

The  white-fly  investigations  now  in  progress  were  begun  in  July, 

1906,  by  the  senior  author,  who  was  in  field  charge  up  to  the  time  of 

his  resignation  from  the  bureau  in  August,  1909,     The  junior  author's 

connection  with  these  investigations  dated  from  June,   1907.     The 

life-history  studies  of  the  first  two  years  have  been  largely  superseded 

by  the  more  extensive  work  of  the  third  year.     Practically  all  of  the 

data  presented  under  the  subjects  of  the  life  history  and  habits  and 

the  seasonal  history  of  each  species  are  based  on  studies  by  the  junior 

author  and  were  written  by  him.     The  remainder  of  the  bulletin  was 

written  by  the  senior  author. 

9 


10  WHITE   FLIES  INJURIOUS   TO   CITRUS   IN   FLORIDA. 

SPECIES  OF  WHITE  FLIES  AFFECTING  CITRUS. 

Twelve  species  and  one  subspecies  of  the  family  Aleyrodidse  are 
known  to  breed  upon  citrus.  The  list  of  these  insects,  the  authority 
for  the  original  description,  the  recorded  distribution,  and  the  food- 
plant  records  are  given  in  Table  I : 

Table  I. — Aleyrodidse  that  breed  upon  citrus. 


Species. 

Described  by — 

Occurrence. 

Food  plants  other  than 
citrus. 

Aleyrodes  citri   (syn.    au- 

rantii).1 
Alevrodes  floccosa 

Riley   and   How- 
ard. 

Maskell 

Quaintance 

Kotinsky 

North  and  South  America, 
Asia,  Japan. 

See  list,  p.  29. 

Aleyrodes  floridensis 

Aleyrodes  giffardi 

United  States  (Florida).... 

Persea  gratissima  (alligator 
pear),  Psidium    guajava 
(guava). 

Quaintance 

do 

Cuba,  United  States  (Flor- 
ida). 
Japan 

Do. 

Alevrodes  marlatti 

Do. 

Alevrodes  mori 

do 

United  States  (Florida)... 
United  States  (Arizona) . . . 
United    States    ( Florida, 
Louisiana),  Cuba. 

Do. 

Alevrodes  mori  arizonensis . 

Cockerell 

Do. 

Aleyrodes  nubifera 

Berger 

Do. 

Quaintance 

Rosa  spp. 

Aleyrodes  struthanthi 

Aleyrodes  vitrinellus 2 

Paraleyrodes  perseae 

Cockerell 

Quaintance 

Mexico 

(struthansus)  flexicaulis. 

United  States  (Florida) 

Do. 

i  Mr.  A.  L.  Quaintance,  after  careful  comparison  of  material  from  Maskell's  collection,  evidently  type 
material,  with  A .  citri,  concluded  that  Maskell's  aurantii  was  the  same  as  Riley  and  Howard's  citri.  Through 
the  kindness  of  Mr.  Quaintance  the  authors  have  had  an  opportunity  to  examine  the  material  referred  to 
and  agree  with  him  in  considering  aurantii  a  synonym  of  citri. 

2  There  seems  to  be  some  doubt  as  to  the  identity  of  the  food  plant  of  this  species,  for  in  connection  with 
the  description  the  authority  for  it  gives  the  following  food  plant  record:  "On  the  under  side  of  leaves  which 
appear  to  be  those  of  orange." 

Of  the  Aleyrodidse  referred  to  above,  A.  citri,  A.  giffardi,  A.  Tiowardi 
(PL  II,  figs.  2,  4),  and  A.  nubifera  are  known  to  be  orange  pests  or 
capable  of  becoming  orange  pests.  A.  floridensis,  A.  mori  (PL  II, 
fig.  I),  A.  mori  arizonensis,  and  Paraleyrodes  persese  (PL  II,  fig.  3) 
apparently  are  not  likely  to  cause  injury  to  citrus,  while  the  remainder 
of  those  listed  are  doubtful  in  this  respect. 

Paraleyrodes  persese  is  found  in  all  sections  of  Florida  and  is  fre- 
quently quite  abundant,  but  in  only  one  instance  has  it  been  known 
to  cause  blackening  of  the  foliage  of  citrus  trees.  This  was  in  the' 
winter  of  1906-7  and  occurred  in  a  pinery  where  in  one  section  citrus 
nursery  trees  were  being  grown.  In  the  course  of  two  or  three  months 
after  being  first  noticed  the  insects  were  reduced  to  the  point  of 
scarcity  through  parasitism  by  a  new  species  of  Encarsia,  which 
Dr.  L.  O.  Howard  has  described  under  the  name  of  Encarsia  variegata. 
Observations  extending  over  three  years  indicate  that  this  parasite 
will  effectively  control  P.  versex  and  that  it  is  unlikely  that  this 
aleyrodid  will  ever  cause  noticeable  injury  under  ordinary  conditions. 
It  is,  however,  possible  that  the  appearance  of  a  prolific  hyperparasite 
of  Encarsia  variegata  might  seriously  interfere  with  the  present  equi- 
librium in  nature. 


Bureau  of  En- 


Plate  II 


Florida  White  Flies  Mistaken  for  Citrus  and  Cloudy-Winged  White  Flies. 

Fig.  1. — Aleyrodes  moH  on  mulberry.  Fig.  2. — Woolly  white  fly  {Aleyrodes howardi)  on  orange. 
Fig.  :i. — Paraleyrodes  persex  on  orange.  Fiur.  L— Woolly  white  fly  {Aleyrodes  howardi), show- 
ing egg<  in  circles  and  adults.    Fig.  5. — Aleyrodes  sp.  on  sea  grape.     (.Original.) 


in  E  CITRUS  WHITE    PL'S  :    11  is  rOBIG  \i-   REVIEW,  1  1 

The  woolly  while  ll\  (Aleyrodes  howardi  Quaintance  (PI.  II,  figs.  2, 
4))  w as  first  discovered  is  this  country  at  Tampa,  Fla.,  I>\  the  junior 
author  in  November,  L909.  The  insect  appears  to  beof  recent  intro- 
duction, since  the  infested  area  has  been  under  observation  at  inter- 
vals during  the  past  three  and  a  half  years  l>>  ili<i  several  men 
connected  with  these  investigations.1 

Ol'  the  four  species  known  to  he  destructive  to  citrus,  Ah yrodes 
citri  and  .1.  nubifi  ra  are  included  in  i  he  invest  igat  ions  herein  reported. 

THE   CITRUS  WHITE  FLY. 

(Aleyrodes  citri  It.  &  ll 

HISTORICAL    REVIEW. 

Origin. 

The  origin  of  the  citrus  white  fly  is  by  circumstances  quite  defi- 
nitely indicated  to  bo  Asiatic.  The  present  known  occurrence  of  it 
in  Japan,  China,  and  India  will  be  referred  to  under  the  subject  of 
distribution.  The  list  of  food  plants,  showing  as  it  does  the  natural 
adaptations  in  this  respect,  indicates  in  itself  that  the  fly  is  not 
native  to  either  North  or  South  America,  but  to  Asia.  Moreover,  if. 
the  citrus  white  fly  were  a  species  native  to  the  Gulf  coast  region  of 
North  America,  or  if  it  had  been  introduced  before  1850,  it  would 
almost  certainly  have  become  a  pest  worthy  of  mention  by  Townend 
Glover  in  his  reports  on  the  orange  insects  of  Florida  published  in  the 
United  States  Agricultural  reports  for  1855  and  1858.  According 
to  these  reports  orange  growing  was  very  extensive  in  proportion  to 
the  population  and  very  profitable  in  spite  of  the  temporary  check 
due  to  the  freeze  of  1835.  The  principal  orange-growing  district  in 
Florida  was,  at  the  time  of  the  reports  of  Glover,  already  mentioned, 
the  northeastern  section  of  the  State,  along  the  St.  Johns  River  and 
at  St.  Augustine.  Orange  growing  on  a  large  scale  gradually  spread  to 
the  south  and  southwest,  the  center  of  production  being  correspond- 
ingly moved.  To-day  citrus  fruits  are  generally  grown  in  all  the 
counties  of  the  peninsula  of  Florida,  yet,  according  to  the  authors' 
estimates,  only  about  40  per  cent  of  the  orange  groves  of  the  State  are 
infested  by  A.  citri.'2.  These  infestations  in  the  different  sections  are 
almost  without  exception  readily  traceable  to  the  ordinary  sources 
of  dissemination,  with  all  the  evidence  strongly  against  the  fly  having 
been  a  native  species  infesting  uncultivated  food  plants.  The  same 
may  be  said  in  regard  to  the  occurrence  of  the  citrus  white  fly  in 
orange-growing  regions  in  Mississippi,  Alabama,  Louisiana,  and  Texas. 

1  The  Woolly  White  Fly,  a  New  Enemy  of  the  Florida  Orange.  Bulletin  G4,  Part 
VIII,  Bureau  of  Entomology,  U.  S.  Department  of  Agriculture,  1910. 

2  A.  nubifera  alone  occurs  in  not  more  than  5  per  cent  of  the  groves.  In  15  of  the 
40  per  cent  above  mentioned  both  A.  citri  and  A.  nubifera  occur. 


12  WHITE   FLIES  INJURIOUS   TO   CITRUS   IN   FLORIDA. 

Early  History  in  the  United  States. 

Riley  and  Howard  give  the  following  account  of  the  status  of  the 
citrus  white  fly  previous  to  1893: 

For  many  years  an  important  and  interesting  species  of  the  type  genus  has  been 
known  to  infest  orange  trees  in  Florida  and  in  more  northern  greenhouses,  and  more 
recently  the  same  form  has  appeared  in  injurious  numbers  in  the  orange  groves  of 
Louisiana.  In  the  Florida  Dispatch,  new  series,  volume  11,  November,  1885,  this 
species  received  the  name  of  Aleyrodes  citri  at  the  hands  of  Mr.  Ashmead.  The  Florida 
Dispatch,  however,  is  a  local  newspaper  of  no  scientific  pretensions,  and  the  descrip- 
tion accompanying  the  name  was  entirely  insufficient  to  enable  recognition  aside  from 
the  food  plant.  We  adopt  the  name  in  connection  with  a  full  description,  not  with  a 
view  of  encouraging  such  mode  of  publication,  which  is  not  sanctioned  by  the  canons 
of  nomenclature  formulated  and  generally  accepted,  but  as  a  manuscript  name,  satis- 
factory in  itself,  the  authority  to  be  recognized  for  it  being  comparatively  immaterial. 

Our  first  acquaintance  with  the  species  was  in  June,  1878,  when  we  found  it  occur- 
ring in  profuse  abundance  on  the  leaves  of  the  citrus  trees  in  the  orangery  of  this 
department.  Some  observations  were  made  upon  its  life  history  during  that  summer, 
and  all  of  its  stages  were  observed.  During  the  following  years  we  observed  it  in 
Florida,  and  it  was  studied  by  two  of  our  agents,  Mr.  H.  G.  Hubbard,  at  Crescent  City, 
and  the  late  Joseph  Voyle,  at  Gainesville.  The  species  was  not  treated  in  Mr.  Hub- 
bard 's  report  on  the  insects  affecting  the  orange,  as  we  wished  to  give  it  a  fuller  consid- 
eration than  could  then  have  been  given,  and  other  duties  prevented  doing  so  in  time. 
Moreover,  at  the  time  when  Mr.  Hubbard's  report  was  prepared  the  insect  had  not 
become  of  especial  economic  importance. 

Since  that  time  many  further  notes  have  been  made  in  Washington,  and  we  have 
received  the  species  from  Pass  Christian,  Miss. ;  New  Orleans,  La. ;  Baton  Rouge,  La. ; 
Raleigh,  N.  C;  and  many  Florida  localities;  and  during  the  past  year  or  two  it  has 
become  so  multiplied  in  parts  of  Louisiana  and  Florida  as  to  deserve  immediate 
attention. 

The  authors  quoted  above  specifically  recorded  the  occurrence  of 
the  white  fly  in  Florida  only  at  Gainesville  (Alachua  County),  Cres- 
cent City  (Putnam  County),1  and  Manatee  (Manatee  County).  Dr. 
H.  J.  Webber  in  1897  (basing  his  statement  on  records  in  1893  and 
1894)  referred  to  the  occurrence  of  the  white  fly  at  the  following  addi- 
tional points:  Evinston  (Alachua  County),  Ocala  and  Citra  (Marion 
County),  Ormond  (Volusia  County),  Panasoffkee  (Sumter  County), 
Orlando  (Orange  County),  Bartow  (Polk  County),  and  Fort  Myers 
(Lee  County) .  Prof.  H.  A.  Gossard  in  1903  mentioned  only  the  follow- 
ing additional  localities  specifically:  Tallahassee  (Leon  County),  Lake 
City  (Columbia  County),  Jacksonville  (Duval  County),  and  Candler 
(Marion  County).     In  the  same  publication  the  following  additional 

1  Examination  of  the  specimens  of  white  flies  in  the  collection  of  the  Bureau  of 
Entomology,  collected  by  Mr.  H.  G.  Hubbard  in  1895  and  bearing  the  locality  label 
"Crescent  City, "  indicate  that  this  record  with  little  doubt  refers  to  Aleyrodes  nubifera. 
Circumstances  known  to  the  authors,  but  which  need  not  be  discussed  here,  show  that 
with  little  doubt  the  citrus  white  fly  was  the  species  present  at  Crescent  City  before 
the  freeze  of  the  winter  of  1894-5.  The  specimens  collected  by  Mr.  Hubbard  probably 
came  from  the  Hubbard  grove  at  Haw  Creek,  several  miles  southeast  of  Crescent  City. 


nil     .1  rRU8    WHIT]     i  i  S  :    BIS!  OBIC  \i     BE1  IE*  .  1  8 

counties  were  reported   more  or  !•'->  infested   without   reference  to 
definite  localities:  Baker,  Jefferson,  Leon,  and  Brevard. 

Messrs.  Rilej  and  Howard  and  Dr.  II.  -I.  Webber  advance  no  theo 
ries  in  regard  t*>  the  original   Florida  infestations.     Prof,  Gossard, 
however,  has  the  following  to  Bay  in  regard  to  the  matter: 

The  il\  seems  to  have  l>««n  fu-i  knon  d  throughout  ili<'  region  comprised  in  Volusia, 
Marion,  Lake,  Alachua,  and  0  mum-,  from  which  I  have  little  or  ao  doubt 

it  was  transferred  to  the  Manatee  country  and  t"  l"<;il  centers  along  the  northern 
borders  of  the  State. 

According  to  reliable  information  received  from  Mi'.  M.  S.  More- 
man,  of  Switzerland,  Fla.;  Mr.  A.  M.  Terwilliger,  of  Minis,  Fla.,  and 
Mr.  T.  V.  Moore,  of  Miami,  Fla.,  the  citrus  white  fly  appeared  in  the 
northern  part  of  St .  Johns  County  at  a  date  which  indicates  thai  this 
section  was  one  of  the  firsl  or  possibly  the  first  to  be  infested  in  the 
State  of  Florida.  Mr.  Terwilliger  informs  us  that  he  first  observed 
the  white  fly  at  Fruit  Cove  on  the  St.  Johns  River  in  1ST!)  in  a  grove 
of  Large  seedling  trees  owned  by  Col.  McGill.  The  McGill  grove 
adjoined  the  grove  of  the  Rev.  T.  W.  Moore,  whose  son,  Mr.  T.  \\ 
Moore,  corroborates  Mr.  Terwilliger  on  the  point  of  the  occurrence 
of  the  white  fly  in  this  section  prior  to  1880.  According  to  Mr. 
Moreman  the  white  fly  was  known  in  the  vicinity  of  Switzerland  on 
the  St.  Johns  River  in  1882,  and  was  first  discovered  in  his  own  grove 
in  1888.  The  species  concerned  is  with  little  douht  the  citrus  white 
fly,  A.  citri,  for  the  authors  and  Mr.  W.  W.  Yothers  have  been  unable 
to  find  specimens  of  any  other  species  at  Switzerland  or  St.  Augus- 
tine, the  two  points  visited  in  the  northern  part  of  St.  Johns  County, 
or  at  Green  Cove  Springs,  located  a  few  miles  below  Switzerland  on 
the  west  side  of  the  St.  Johns  River  in  Clay  County.  These  early 
reports  of  the  citrus  white  fly  in  this  section  of  the  State  are  supported 
by  the  fact  that  the  earliest  collected  specimens  of  this  species  in  the 
collection  of  the  Bureau  of  Entomology  bear  the  date  1888  and  the 
locality  label  "St.  Nicholas,"  a  point  located  in  Duval  County  about 
15  miles  north  of  Fruit  Cove. 

Interesting  information  concerning  the  early  history  of  white-fly 
infestations  in  Florida  has  been  obtained  from  Messrs.  Borland  and 
Kells,  citrus  growers  at  Buckingham,  Lee  County,  Fla.,  formerly  of 
Citra,  Marion  County.  According  to  these  gentlemen,  the  presence 
at  or  near  Panasoffkee,  in  Sumter  County,  Fla.,  of  a  small  white 
insect  which  caused  blackening  of  the  foliage  of  orange  trees  became 
known  among  orange  growers  around  Citra,  at  that  time  in  the 
heart  of  the  orange-growing  district  of  Florida,  in  1881  or  1882. 
The  grove  of  Bishop  Young,  of  Panasoffkee,  was  one  of  the  first 
reported  infested.  It  is  believed  that  Bishop  Young,  after  traveling 
in  Asia  (Palestine?),  brought  back  with  him  plants  which  he  set  out, 
and  in  a  year  or  two  thereafter  blackening  of  the  foliage  of  near-by 


14  WHITE    FLIES   INJURIOUS    TO    CITRUS   IN    FLORIDA. 

citrus  trees  in  association  with  a  new  insect  pest  first  became  notice- 
able. The  white  fly  affecting  citrus  trees  at  Panasoffkee  was  exter- 
minated by  the  freeze  of  1894-1895  and,  so  far  as  the  authors  can 
Lea  in,  has  not  reappeared.  There  seems  to  be  at  present  no  means  of 
determining  whether  the  report  given  above  refers  to  the  citrus 
white  fly  or  to  the  cloudy-winged  white  fly. 

Mr.  A.  J.  Pettigrew,  of  Manatee,  Fla.,  a  reliable  observer  who  has 
been  in  the  citrus  nursery  and  orange-growing  business  in  Manatee 
County  since  1884  and  who  has  been  familiar  with  the  white  fly  since 
its  first  discovery  in  that  country,  has  furnished  the  authors  with  a 
statement  concerning  the  early  history  of  the  pest  in  that  section  of 
Florida.  According  to  Mr.  Pettigrew,  Messrs.  C.  H.  Foster  and  F.  X. 
Horton  each  received  from  Washington,  D.  C,  6  tangerine  trees  in 
1886  or  1887 — as  near  as  can  be  determined  at  this  time,  although 
possibly  earlier  by  a  year  or  two.  A  year  or  two  after  the  trees  were 
received  and  planted,  the  fly  was  noted  by  Mr.  Pettigrew  as  abundant 
on  a  rough  lemon  near  one  of  these  tangerines,  and  the  following  year 
it  was  first  noted  as  abundant  in  a  seedling  orange  grove  near  by. 
At  Mr.  Pettigrew's  suggestion  specimens  were  sent  to  the  Department 
of  Agriculture  at  Washington  and  identified  as  a  white  fly.  These 
specimens  were  probably  sent  to  Washington  in  1891,  for  a  letter 
from  Mr.  Foster,  dated  January  8  of  that  year,  was  published  in 
Insect  Life1  with  the  reply.  The  oldest  specimens  of  the  citrus 
white  fly  now  in  the  collection  of  this  bureau,  which  were  collected 
in  Manatee  County,  Fla.,  bear  the  date  of  March  5,  1891,  with  "Man- 
tee"  as  the  locality  record.  These  were  probably  sent  in  by  Mr. 
Foster  in  connection  with  later  correspondence  than  that  referred 
to  above. 

Concerning  the  history  of  the  citrus  white  fly  in  Louisiana,  Prof. 
H.  A.  Morgan  in  1893  made  the  following  statement: 

This  pest,  common  from  Baton  Rouge  to  the  Gulf,  is  known  as  the  white  fly.  Orange 
grpwera  claim  that  it  has  been  recently  introduced — that  is,  within  the  last  ten  years — 
and  it  is  supposed  to  have  come  in  upon  plants  brought  to  the  New  Orleans  exposition 
in  the  year  1885.  The  present  wide  distribution  of  the  white  fly  in  the  southeastern 
United  States  is  due  to  the  lack  of  restrictions,  until  very  recently,  against  shipments 
of  infested  nursery  stock  and  of  privets  and  the  Cape  jessamine. 

Literature. 

The  citrus  white  fly  was  first  given  a  valid  scientific  name  and 
adequately  described  by  Riley  and  Howard  in  an  article  published 
in  Insect  Life2  in  April,  1893.  Following  the  account  of  the  early 
history  heretofore  quoted,  these  authors  describe  the  different  stages 
of  the  insect  in  detail,  give  an  account  of  the  habits  and  life  history, 
and  give  records  with  discussion  of  results  obtained  by  a  correspondent 

1  Insect  Life,  vol.  4,  p.  274.  2Id.,  vol.  5,  no.  4,  pp.  219-226,  1893. 


tin-  ciTBua  n\  ii 1 1 1    ply:  histobu  u.  review.  LS 

in   Manatee  County,   Fla.,   \\\\*>  had   undertaken  some  cooperative 
experiments  in  spraying. 

During  the  same  year  (1893)  Prof.  1 1.  A.  Morgan,  then  entomolo 
of  the  Louisiana  Agricult  urn  I  Experiment  Station,  lm\  e  an  account  of 
the  citrus  white  il\  in  Louisiana  in  a  bulletin  of  that  Btation.1 

The  Division  of  Vegetable  Physiology  and  Pathology  <>l*  ili<i  United 
States  Department  of  Agriculture  began  investigations  of  citrus 
diseases  in  Florida  in  1893.  These  included  investigations  of  the 
"sooty  mold"  resulting  from  white-fly  infest  .-it  ion,  and  the  first  report 
on  the  subject  was  published  by  Swingle  and  Webber  in  L896a  and  a 
more  extended  report  by  Dr.  II.  J.  Webber  in  1M)7.:!  Conclusions 
from  B  series  of  spraying  experiments  are  included  in  this  publica- 
tion and  many  important  observations  are  recorded,  particularly  in 
connection  with  the  two  most  useful  fungous  enemies  of  the  white  fly 
which  were  discovered  by  Dr.  Webber  in  the  course  of  his  work. 

Prof.  II.  A.  Gossard,  then  entomologist  of  the  Florida  Agricultural 
Experiment  Station,  published,  in  1903,4  an  account  of  the  white  fly 
situation  up  to  that  time,  with  his  conclusions  from  observations 
extending  over  several  years. 

In  a  volume  entitled  "Citrus  Fruits,"  published  in  1904  by  Prof. 
H.  II.  Hume,  four  chapters  are  devoted  to  citrus  insect  pests  and 
methods  of  control,  the  white  fly  receiving  due  attention. 

Since  the  present  investigations  by  the  Bureau  of  Entomology  have 
been  in  progress,  Dr.  Berger,  entomologist  of  the  Florida  Experiment 
Station,  has  published  two  bulletins5  winch  present  a  summary  of 
white-fly  conditions  with  recommendations  for  control,  particularly 
with  reference  to  the  use  of  fungous  enemies.  In  the  later  pub- 
lished of  the  two  mentioned,  the  specific  distinctions  are  pointed  out 
and  illustrated,  separating  from  the  common  A.  citri  the  form  which 
Dr.  Berger  has  named  A.  nubifera. 

Messrs.  P.  II.  Rolfs  and  H.  S.  Fawcett,  in  a  bulletin  issued  in  July, 
1908,8  discuss  in  a  general  way  the  use  of  fungous  parasites  of  the  white 
fly  in  Florida  and  give  recommendations  for  the  introduction  of  the 
three  most  common  species.  The  most  important  contribution  to  our 
knowledge  of  the  fungous  parasites  of  the  citrus  white  fly  is  contained 
in  a  paper  by  Prof.  H.  S.  Fawcett,  published  in  1909.7 

1  The  Orange  and  Other  Citrus  Fruits.  By  W.  C.  Stubbs  and  H.  A.  Morgan.  Spec. 
Bui.  La.  Agr.  Exp.  Shi.,  pp.  7L-73,  1893. 

2  The  Principal  Diseases  of  Citrus  Fruits  in  Florida.  By  W.  T.  Swingle  and  H.  J. 
Webber.     Bui.  8,  Division  of  Vegetable  Physiology  and  Pathology,  pp.  25-28,  1896. 

3  The  Sooty  Mold  of  the  Orange  and  its  Treatment.  Bui.  13,  Division  of  Vegetable 
Physiology  and  Pathology,  U.S.  Department  of  Agriculture,  1897. 

4  White  Fly.     Bui.  67,  Fla.  Agr.  Exp.  Sta.,  June,  1903. 

5  White  Fly  Conditions  in  1906,  the  Use  of  Fungi.  Bui.  88,  Fla.  Agr.  Exp.  Sta.,  Jan- 
uary, 1907;  White  Fly  Studies  in  1908,  Bui.  97,  Fla.  Agr.  Exp.  Sta.,  February,  1909. 

6  Bui.  94,  Fla.  Agr.  Exp.  Sta.,  July,  1908. 

7  Special  Studies  No.  1,  University  of  State  of  Florida,  1909. 


16  WHITE    FLIES   INJURIOUS   TO   CITRUS   IN   FLORIDA. 

Tn  Louisiana  the  demand  for  information  concerning  the  citrus 
while  fly  has  resulted  in  a  publication  on  this  subject  by  Mr.  A.  II. 
Rosenfeld  in  1907.1  The  discovery  of  the  white  fly  in  California  in 
the  same  year  led  to  the  publication,  by  Prof.  C.  W.  Wood  worth,  of  a 
circular  of  general  information,2  and  of  a  second  circular  f  dealing 
with  the  methods  of  eradication  that  were  being  employed  i:i  that 
State.  A  very  complete  account  of  the  white-fly  infestation  in  Cali- 
fornia was  given  by  Mr.  C.  L.  Marlatt,  assistant  entomologist  of  th<i 
Bureau  of  Entomology,  before  the  Entomological  Society  of  Wash- 
ington.4 

The  foregoing  paragraphs  refer  to  the  principal  publications  in 
which  the  citrus  white  fly  is  treated,  exclusive  of  short  papers  in  hor- 
ticultural periodicals,  press  bulletins,  experiment  station  reports,  and 
transactions  of  the  Florida  State  Horticultural  Society.  Numerous 
press  bulletins  have  been  issued  by  the  Florida  State  Experiment  Sta- 
tion dealing  with  several  phases  of  white-fly  control  and  written  from 
time  to  time  as  the  occasion  demanded  by  Prof.  Gossard,  Dr.  Sellards 
Dr.  Berger,  and  Prof.  Fawcett. 

Reviews  of  the  white-fly  situation  for  the  year,  with  notes  on  new 
observations,  have  been  included  in  their  annual  reports  by  each  of 
the  first  three  named,  who  have  served  successively  as  entomologist 
at  the  Florida  Experiment  Station.  Many  important  papers  and  dis- 
cussions on  the  white  fly  have  been  published  in  the  Transactions  of 
the  State  Horticultural  Society,  but  for  the  most  part  these  have 
been  incorporated  or  the  ground  covered  more  fully  in  the  regular 
bulletins  referred  to. 

Taken  as  a  whole,  the  literature  on  the  citrus  white  fly  is  quite 
extensive,  giving  a  fairly  good  idea  of  the  status  of  the  white  fly  and 
progress  in  methods  of  control  from  year  to  year  since  the  publi- 
cation of  the  paper  by  Riley  and  Howard  referred  to  in  the  opening 
paragraph. 

The  description  of  the  different  stages  and  the  account  of  the  life 
history  and  habits  of  the  citrus  white  fly  by  Riley  and  Howard  have 
been  followed  quite  closely  by  subsequent  writers,  few  additional 
records  having  been  made  up  to  the  beginning  of  the  present  investi- 
gations. Records  of  food  plants,  miscellaneous  life-history  records, 
general  results  of  field  experiments,  and  conclusions  from  general 
observations  on  the  efficiency  of  spraying,  fumigating,  and  natural 
control  by  fungous  diseases  have  been  published  by  Messrs.  H.  J. 
Webber,  H.  A.  Gossard,  E.  H.  Sellards,  E.  W.  Berger,  and  H.  S. 
Fawcett.     Comparatively  little  real  data  has  been  published  so  far  in 

1  Circular  18,  State  Crop  Pest  Commission  of  Louisiana,  1907. 

2  Circular  30,  California  Agricultural  Experiment  Station,  1907. 

3  Circular  32,  California  Agricultural  Experiment  Station,  1907. 

4  Proceedings  of  the  Entomological  Society  of  Washington,  vol.  9,  pp.  121-123,  1908. 


ill  I.   CITBUS    WHITE  FLY:  INJURY.  17 

connection  with  experimental  work  with  the  white  fly,  A  review  of 
all  t lio  literature  to  date  shows  that  data  have  been  published  on  the 

effect  of  kerosene  enniUion  on  while-lly  eggs,  by  Iviley  and  Howard; 
on  the  subject   of  effects  of  cold   upon  white  -fly   larva*  and   |>ii|>a\   by 

Prof.  Gossard;  on  the  percentage  of  trees  infected  by  the  spore- 
Bpraying  hum  hod  of  introducing  the  fungous  parasites,  and  on  the 

amount  o(  honeydew  secreted  by  the  larva*  of  the.  insect,  by  Dr.  E.  \V. 
Berger;  upon  subjects  related  to  fumigation,1  by  (he  senior  ant  hoi- of 
the  present  bulletin;  and  on  laboratory  experiments  with  the  fungous 
parasites,  by  Prof.  H.  S.  Fawcett.  Aside  from  the  above,  practical  I  v 
no  data  have  been  heretofore  published. 

INJURY. 

Nature  of  Injury. 

The  direct  injury  by  the  citrus  white  fly  may  be  included  under 
two  main  heads:  (1)  Injury  by  removal  of  sap  from  foliage,  and  (2) 
injury  from  fungous  growth  known  as  sooty  mold  (Meliola),  which 
develops  upon  foliage  and  fruit  on  the  excretions  of  the  insects. 

The  direct  injury  is  principally  included  as  loss  in  value  of  trees, 
extra  expenses  of  maintenance,  and  losses  from  scale  insects  and  dis- 
eases, which  more  seriously  affect  white-fly  infested  trees. 

LOSS    OP    SAP. 

The  amount  of  sap  extracted  by  the  insects  is  not  generally  con- 
sidered an  item  of  great  importance  compared  with  the  injur}^  from 
sooty  mold.  While  the  extraction  of  sap  by  itself  probably  would 
not  cause  sufficient  injury  to  make  the  white  fly  rank  as  an  important 
citrus  pest,  it  is  doubtless  of  considerable  importance  when  combined 
with  the  lowered  assimilative  powers  of  the  foliage  due  to  the  sooty 
mold.  As  mentioned  more  in  detail  under  the  subject  of  feeding 
habits,  it  has  been  estimated  that  the  loss  of  sap  per  day  amounts  to 
about  one-half  of  a  pound  for  1,000,000  larvae  and  pupae. 

SOOTY  MOLD. 

Sooty  mold  is  the  principal  evidence  of  white-fly  injury,  and  is  the 
most  important  element  of  damage,  affecting  both  the  foliage  and  fruit. 
(See  PL  I,  frontispiece.)  No  special  attention  has  been  given  by  the 
authors  to  its  botanical  aspects,  but  the  following  notes  concerning  it 
are  taken  mainly  from  Dr.  H.  J.  Webber's  report  on  this  subject:2 

1  Fumigation  for  the  Citrus  White  Fly  as  adapted  to  Florida  Conditions.  Bulletin 
76,  Bureau  of  Entomology,  U.  S.  Department  of  Agriculture,  Oct.  31,  1908. 

2  Bulletin  13,  Division  of  Vegetable  Physiology  and  Pathology,  U.  S.  Department 
of  Agriculture,  pp.  5-11,  1897. 

86850°—  Bull.  92—11 2 


18  WHITE    l'UKS    [NJUKIOUS    TO   CITRUS    IN    FLORIDA. 

The  Booty-mold  fungus  is  a  species  of  the  genus  Meliola1  of  the 
order  Pyrenomycetes.  Dr.  Webber  states  that  in  Florida  and  Loui- 
siana it  is  quite  generally  known  as  smut  or  black  smut,  but  as  the 
fungus  concerned  is  not  a  smut  fungus  these  terms  are  erroneous, 
and  t  heir  use  should  be  discontinued.  When  abundant  on  leaves  and 
fruit  of  citrus,  this  fungus  forms  a  dark-brown  or  black  membranous 
coating  composed  of  densely  interwoven  branched  mycelial  filaments. 
At  first  this  coating  covers  only  limited  spots  or  is  not  thick  enough 
to  form  a  distinct  membrane,  but  later,  if  the  honey  dew-secreting 
insects  are  abundant,  the  coating  becomes  thick  enough  to  be  entirely 
removed  from  the  leaf  and  torn  like  paper.      (PI.  Ill,  figs.  1,2.) 

Frequently  the  fungus  membrane  becomes  detached  at  some  point 
and  is  caught  by  the  wind  and  large  fragments  torn  off.  These 
fungus  fragments  are  found  scattered  about  in  badly  infested  groves 
in  the  fall,  being  especially  noticeable  during  the  winter  after  a  high 
wind  or  after  the  trees  have  been  sprayed. 

Dr.  Webber  recognized  several  forms  of  reproductive  agents,  which 
are  easily  distributed  by  various  means,  but  principally  by  winds. 
The  fungus  is  entirely  saprophytic  in  so  far  as  known,  deriving  its 
nourishment  from  the  honeydew  secreted  by  certain  insects.  As  such 
honeydew  falls  mostly  on  the  upper  surface  of  the  leaves  and  on  the 
upper  half  or  stem  end  of  the  fruit,  the  sooty  mold  develops  most 
densely  in  these  places,  but  it  is  usually  present  to  a  greater  or  less 
extent  on  the  lower  surface  of  the  leaves,  sometimes  developing  in 
tufts  on  drops  of  honeydew  which  diseased  insects  fail  to  expel  in  a 
normal  manner.  Sooty  mold  also  develops  on  the  twigs  and  in 
some  cases  on  the  sides  of  buildings  when  heavily  infested  trees  are 
growing  near  by. 

Seasonal  history  of  sooty  mold. — The  sooty  mold  resulting  from  the 
attacks  of  the  citrus  white  fly  is  most  abundant  late  in  the  season. 
Very  little  sooty  mold  develops  during  the  winter  months,  while  the 
films  of  blackish  mycelium  gradually  become  removed  from  the  leaves 
by  winds  and  rains  and  much  is  knocked  off  in  picking  the  fruit,  in 
spraying,  pruning,  fumigating,  etc.  The  thicker  the  coating  of  sooty 
mold,  the  more  readily  and  thoroughly  it  is  removed.  By  the  time 
of  the  appearance  of  the  new  spring  growth  the  greater  part  of  the 
sooty  mold  on  the  old  leaves  has  disappeared  and  from  this  time  to 
the  1st  of  May  there  is  very  little,  if  any,  evidence  of  a  new  growth 
of  this  fungus.  Slight  blackening  of  spring  growth  has  been  noted 
as  far  north  as  Island  Grove  in  Alachua  County,  Fla.,  as  early  as 
May  20,  the  average  number  of  live  larvae  and  pupae  per  leaf  being 
estimated  as  about  50,  not  including  old  leaves  which  were  practically 
uninfested.     By  June  20,  leaves  from  Mcintosh,  in  the  same  county, 

1  Generally  referred  to  M.  camellia  (Catt.)  Sacc.,  but  perhaps  including  more  than 
one  speci' 


Plate  III. 


Sooty  Mold. 

Fig.  1.— Sooty  mold  on  orange  leaf  following  white-fly  attack:  broken  and  falling  from  leaf. 
Fig.  2.— Sooty  mold  on  cinnamon  tree  following  attacks  by  cinnamon  scale.     (Original.) 


I  in:   CITRUS    WHITE  PLY:  INJURY.  1  9 

with  an  average  of  about  11  live  larv©  and  pupa  cases1  per  leaf,  were 
slightly  blackened.  In  general,  heayj  coats  of  soot)  mold  on  leaves 
are  common  in  Florida  l>v  the  Isl  of  June  in  groves  heavily  infe  ted 
hv  i  he  tit  rus  w  hite  fly. 

Effect  of  sooty  mold  on  leaf  functions.  Dr.  Webber  has  discussed 
the  effect  of  sooty  mold  on  leaf  functions  in  the  report  already  referred 
to,  and  as  t  he re  i>  nothing  to  add  at  t  Ins  time,  the  following  paragraph 
(pp,  10   LI)  is  quoted : 

When  ii  Lb  remembered  thai  various  investigations  have  shown  thai  the  proc< 
ph)  tosj  max    i-  almost  entirely  checked  in  a  plant  placed  in  the  back  pari  of  a  living 
room,  opposite  a  window,  where  the  lighl  is  fairly  bright,  bu1  diffused,  Li  can  readily 

be  judged  that  tin1  effect  of  the  dark,  compact  mycelial  membrane  of  tin-  sooty  mold 
covering  the  Leaves  would  be  to  almost  wholly  check  the  process  of  phytosyntax  in  the 
orange  tree.  Quite  bright  or  direct  sunlight  is  necessary  for  the  besl  results.  The 
injurious  effects  of  Booty  mold  on  the  phytosyntax  wasclearly  demonstrated  by  Busgen. 
He  removed  the  fungus  membrane  from  a  small  portion  of  a  leaf  and  exposed  the  leaf 
to  the  sun.  In  the  evening,  after  a  sunny  day,  the  leaf  was  plucked  and  the  chlorophyll 
extracted  with  alcohol.  After  this  leaf  was  treated  with  iodine,  the  parts  from  which 
the  membrane  had  been  removed  in  every  case  stained  a  dense  blue,  indicating  the 
formation  of  an  abundance  of  starch,  while  the  surrounding  portions  of  the  leaf,  which 
were  protected  from  the  sun  by  the  fungus  membrane,  remained  entirely  uncolored, 
showing  that  no  starch  was  formed.  The  stomata,  or  breathing  pores,  are  also  to  some 
extent  closed  by  the  sooty  mold,  and  in  this  way  the  passage  of  gas  is  more  or  less 
hindered.  In  the  orange  leaf,  however,  the  stomata  are  confined  to  the  lower  surface, 
where  generally  there  is  but  little  sooty  mold.  In  plants  where  the  stomata  are  on  the 
upper  surface  of  the  leaf  also,  the  damage  resulting  from  the  obstruction  of  the  passage 
of  gases  would  probably  be  considerably  greater. 

Extent  of  Injury. 

In  the  following  discussion  the  statements  concerning  injury  and 
the  estimates  of  the  extent  of  this  injury  by  the  citrus  white  fly  refer 
to  groves  in  which  the  fly  has  become  well  established  and  in  which 
no  remedial  measures  have  been  practiced. 

INJURY   TO    FRUIT. 

Unless  otherwise  stated,  oranges  and  tangerines  are  referred  to. 
These  constitute  more  than  88  per  cent  of  the  citrus  fruit  crop  of 
Florida.  The  total  injury  to  grapefruit  by  the  citrus  white  fly  i> 
rarely  over  15  per  cent  and  is  frequently  inappreciable. 

Ripening  retarded. — Ripening  of  fruit  on  heavily  infested  citrus  trees 
is  greatly  retarded,  and  in  case  of  the  formation  of  a  very  heavy  coat- 
ing of  sooty  mold  on  the  upper  half  of  the  orange  the  rind  underneath 
it  may  remain  green  indefinitely  while  the  lower  half  of  the  fruit  is 

1  Some  of  the  first  generation  had  matured,  but  are  properly  included  with  the 
insects  responsible  for  the  sooty  mold  present. 

2  "  Phytosyntax ' '  refers  to  the  process  of  the  formation  of  complex  carbon  compounds 
out  of  simple  ones  under  the  influence  of  light;  '  'photosynthesis' '  is  a  more  common 
term  for  this  process  of  assimilation. 


20  WHITE   FLIES   INJURIOUS   TO   CITRUS   IN    FLORIDA. 

well  colored.  The  retardation  of  ripening,  delaying  as  it  does  in  some 
cases  the  time  when  the  fruit  is  marketable  and  materially  increasing 
the  percentage  of  culls,  causes  injury  which  is  very  conservatively 
estimated  to  range  from  2  to  5  per  cent  of  the  value  of  the  crop.  The 
injury  to  grapefruit  in  retardation  of  ripening  by  the  citrus  white  fly 
is  much  less,  varying  from  none  at  all  to  2  or  3  per  cent. 

Number  and  size. — The  greatest  injury  by  the  white  fly  is  in  the 
reduction  of  the  salable  crop  of  fruit.  Dr.  Webber  on  this  point 
makes  the  following  statement  :l 

The  effect  of  the  sooty  mold  on  the  orange  is  very  noticeable,  the  growth  being 
usually  greatly  retarded  and  the  blooming  and  fruiting  light.  In  serious  cases  growth 
is  frequently  entirely  checked,  and  blooming  and  fruiting  wholly  suppressed  until 
relief  is  obtained. 

Prof.  Gossard  has  estimated  2  that  during  a  six-year  period  the 
reduction  in  yield  due  to  the  citrus  white  fly  is  from  25  to  40  per  cent. 

Replies  to  a  circular  letter  of  inquiry  addressed  to  orange  growers 
and  the  observation  of  the  authors  in  Florida  indicate  that  the  reduc- 
tion in  yield  due  to  the  citrus  white  fly  amounts  to  50  per  cent,  on 
the  average,  when  no  artificial  methods  of  control  are  practiced. 

From  information  received  from  many  growers  and  from  personal 
observation,  the  authors  would  estimate  that  with  continued  good  care 
and  with  the  additional  fertilizer  usually  given  infested  trees  the 
reduction  in  yield  in  different  groves  in  a  series  of  years  amounts  to 
an  average  between  20  and  50  per  cent. 

The  decrease  in  yield  due  to  white-fly  infestation  ordinarily  consists 
of  a  decrease  in  the  actual  number  of  fruit  produced  and  also  in  the 
packing  size.  From  information  obtained  it  seems  a  conservative 
estimate  to  consider  that  oranges  and  tangerines  are  reduced  either 
one  or  two  packing  sizes  as  a  result  of  white-fly  attack.  For  each 
packing  size,  the  number  of  reduced  fruit  remaining  the  same,  the 
reduction  in  the  crop  would  average  about  12.5  per  cent. 

Expense  of  cleaning. — Fruit  noticeably  affected  with  sooty  mold 
requires  cleaning  before  marketing.  One  of  the  most  economical 
machines  for  washing  fruit  used  in  Florida  is  a  California  washer  used 
by  Mr.  F.  D.  Waite,  of  Palmetto,  and  Mr.  F.  L.  Wills,  of  Sutherland. 
The  cost  of  washing  with  these  machines  ranges  from  1.4  to  2.5  cents 
per  box.  The  cost  of  cleaning  with  the  simplest  machines  is  about 
5  cents  per  box.  Mr.  E.  H.  Walker,  of  Orlando,  Fla.,  estimates  the 
cost  of  hand  cleaning  oranges  at  10  cents  per  box  as  a  minimum  and 
7  cents  a  box  for  cleaning  grapefruit.  In  consideration  of  the  fore- 
going it  is  estimated  that  the  range  in  cost  of  cleaning  the  sooty 
mold  from  fruit  to  be  from  1  to  10  per  cent  of  the  value  of  the  crop. 

Shipping  and  Jceeping  quality. — The  sooty  mold  produced  by  the 
white  fly  and  other  citrus  pests  does  not,  so  far  as  known,  affect  the 

1  Loc.  cit.,  p.  9.  2  Bui.  67,  Fla.  Agr.  Exp.  Sta.,  p.  617. 


ill  r   CITRUS    w  II  n  i     FLY:    inn  Rl  . 


21 


shipping  quality  of  the  Fruit  directly,  but  the  processes  of  cleaning 
have  been  proved  to  be  of  considerable  importance  in  this  respect. 
The  subject  of  the  deterioration  in  shipping  quality  <»f  citrus  fruits 
has  been   thoroughly   investigated   in  California    by   agents  of  the 

Bureau  of  Plant  Industry  under  the  direction  of  Mr.  (i.  II.  Powell.1 
Their  report  shows  in  a  conclusive  manner  that  the  amount  of  decay 
in  shipment  is  very  materially  increased  by  brushing  or  washing  tin* 
Fruit  to  remove  the  Bootj  mold.  Table  II,  arranged  from  data  pub- 
lished in  the  report  referred  to,  shows  the  effect  of  dry  brushing  and 
washing  fruit  on  the  percentage  of  decay. 

Table  II. — Effect,  on  decay,  of  cleaning  sooty  mold  from  fruit. 


Record 
No. 

Unbrushed 

fruit  ap- 
parently 
sound. 

Dry 

brushed 

fruit  ap- 
parently 
sound. 

Washed 
fruit  ap- 
parently 
sound. 

1 

2 

3 

Per  cent. 
2.  7 
1.9 

Per  cent. 
6.6 

4.2 
1.8 

Per  cent. 
17.8 
10.0 
2.6 

It  will  be  observed  that  dry  brushing  increased  the  amount  of 
decay  to  about  two  and  one-half  times  the  decay  in  the  unbrushed  in 
record  No.  1,  and  to  about  two  and  one-fifth  times  in  record  No.  2. 
Washing  increased  the  amount  of  decay  to  about  six  and  two-thirds 
times  in  record  No.  1,  and  to  about  five  and  one-fifth  times  in  record 
No.  2. 

The  injury  from  cleaning  the  fruit  is  due  to  the  increased  opportu- 
nities for  infection  with  spores  of  the  blue  mold  and  to  mechanical 
injuries  in  the  process  of  cleaning.  The  chances  of  decay  are  still 
further  increased  whenever  the  fruit  is  not  thoroughly  dried  before 
packing.  Washing  in  constantly  running  water  or  by  running  the 
fruits  through  brushes  with  water  constantly  sprayed  over  them  is 
considered  much  less  objectionable  than  the  ordinary  systems. 

Flavor. — The  attack  of  the  white  fly  is  generally  supposed  to  affect 
the  quality  of  the  fruit  in  a  marked  degree.  Dr.  Webber  and  Prof. 
Gossard  describe  the  flavor  as  insipid  as  a  result  of  heavy  infestations. 
The  latter  presents  the  results  of  chemical  analyses  of  samples  of  the 
fruit  of  tangerine  trees  in  two  adjoining  groves.  In  one  grove  the 
white  fly  was  completely  controlled  by  spraying;  in  the  other  the  fly 
was  unchecked.  The  analyses  showed  that  there  was,  in  the  samples 
from  the  latter  grove,  15  per  cent  less  reducing  sugar,  15  per  cent 
less  sugar  dextrose,  and  5  per  cent  less  citric  acid.  While  oranges 
and  tangerines  are  frequently  much  affected  in  flavor,  thoroughly 
blackened  groves  in  many  cases  produce  as  well  flavored  fruit  as  can 


1  Bulletin  123,  Bureau  of  Plant  Industry,  U.  S.  Department  of  Agriculture. 


22  WHITE   FLIES   INJURIOUS   TO   CITRUS   IN    FLORIDA. 


be  found  in  the  market.  When  trees  are  supplied  with  as  much 
fertilizer  as  they  can  use  to  advantage  the  white  fly  does  not  ordi- 
narily affect  the  flavor  of  the  fruit  to  such  a  noticeable  extent  as  is 
commonly  believed.  It  is  suspected  that  a  well-grounded  prejudice 
against  the  white  fly  rather  than  a  discriminating  taste  is  responsible 
for  a  large  part  of  the  supposed  effect  on  the  flavor  of  the  fruit  in 
infested  groves. 

Increased  injury  from  scale  insects  and  from  'plant  diseases. — The 
number  of  culls  is  in  some  cases  very  much  increased  by  diseases  and 
insect  pests  which  thrive  after  the  trees  have  been  weakened  by  the 
white  fly.  There  are  no  data  available  showing  the  usual  increase  in 
percentage  of  fruit  injured  by  scales  and  by  diseases  of  the  trees  as 
a  result  of  white-fly  infestation,  but  this  is  a  consequence  observed 
by  many  citrus  growers  and  is  properly  considered  a  factor  of  white-fly 
injury.  As  such  it  is  conservatively  estimated  to  vary  from  1  to  5 
per  cent  in  groves  thoroughly  infested,  although  an  instance  of  a 
valuable  crop  being  completely  ruined  by  secondary  scale  attack  has 
come  under  the  authors'  observation. 

Market  value. — Imperfections  in  fruit  rind  due  to  diseases  and 
insect  pests  as  followers  of  the  white  fly  and  to  failure  of  fruit  rind  to 
color  up  normally,  in  addition  to  the  direct  effect  on  the  size  of.  the 
marketable  crop  as  heretofore  discussed,  usually  lower  the  average 
grade  even  after  the  fruit  is  cleaned  by  the  most  approved  methods. 
A  few  growers  claim  that  after  being  cleaned  their  oranges  and  tanger- 
ines bring  as  good  prices  as  any,  and  leaving  out  of  consideration 
instances  where  it  is  claimed  that  most  or  all  of  the  fruit  is  rendered 
absolutely  unsalable  under  any  conditions,  we  may  conservatively 
estimate  the  depreciation  in  market  value  to  range  from  none  at  all 
to  10  per  cent. 

Sooty-mold-blackened  oranges  shipped  without  cleaning  have  a 
market  value  ordinarily  from  25  to  50  cents  less  per  box  than  the 
same  fruit  would  have  cleaned.1  Certain  Florida  brands  of  oranges 
well  advertised,  carefully  graded,  and  packed,  would  fail  to  bring  within 
a  dollar  a  box  of  their  average  value  if  they  appeared  on  the  market 
blackened  by  sooty  mold. 

Losses  to  growers  estimated  on  basis  of  prices  paid  by  orange  buyers. — 
The  authors  are  indebted  to  Mr.  E.  H.  Walker,  of  Orlando,  for  the 
information  that  during  the  season  of  1907-8  orange  buyers  in  Florida 
paid  from  $0.75  to  $1.45  for  oranges  free  from  white-fly  effects,  and 
from  $0.50  to  $1  per  box  for  fruit  blackened  by  white  fly;  during 
the  season  of  1908-9  the  price  paid  for  clean  fruit  varied  from  $0.60 
to  $1  per  box,  and  from  $0.50  to  $0.75  for  fruit  blackened  by  sooty 
mold.     The  loss  to  the  growers  is  not  entirely  represented  by  these 

1  Statement  based  on  information  from  Mr.  E.  H.  Walker,  Orlando,  Fla. 


I  II  I     CITRUS    whim     PLY  :    I  N.l  i  'i:\ 


23 


figures,  Bince,  according  to  Mr.  Walker,  the  beet  prices  were  not  paid 
for  Boot}  mold  blackened  fruit  until  late  m  the  season  after  the  clean 
fruit  had  nearly  all  been  shipped  or  disposed  of.  Clean  fruit  at  this 
time*  would  have  been  proportionally  more  profitable. 

ivm  Rl     i<>    i  1:1  i  - 

Weakening  oj  vitality.  It  is  doubtful  if  the  while  fly  is  ever  the 
direct  cause  of  the  killing  of  trees,  limbs,  or  twigs  in  well-fertilized 
groves.     It  does,  however,  seriously  stunt  the  growth  of  all  heavily 

Infested    tree-,    and    may    temporarily    entirely    cheek    the   growth    of 

young  tree-.  It-  greatest  effect  on  the  vitality  of  the  tree  is  an  indi- 
rect one.  [nfestation  by  the  white  fly  appears  to  weaken  the  resist- 
ance of  orange  and  tangerine  trees  to  foot  rot,  die  hack,  melanose, 
wither  tip,  and  drought,  and  favors  the  multiplication  of  the  purple 
and  long  scales  which  are  second  to  the  citrus  white  fly  as  citrus  pests 
in  the  Gulf  coast  regions. 

Depreciation  in  value. — The  selling  values  of  citrus  groves  are  greatly 
reduced  by  white-fly  infestation,  and  citrus  nurseries  have  their  ter- 
ritory for  sales  much  restricted  and  values  reduced.  Concerning  the 
reduction  in  value  of  groves  of  bearing  trees  one  of  the  most  experi- 
enced dealers  in  orange  groves  in  the  State  estimates  that  it  is  in 
general  about  one-third.  For  years  California  has  been  closed  to 
Florida  nurserymen  as  a  field  for  the  sale  of  citrus  nursery  trees,  and 
a  similar  quarantine  regulation  has  recently  gone  into  effect  in  Ari- 
zona. In  Florida  and  in  citrus-growing  sections  of  other  Gulf  coast 
States  a  guaranty  of  freedom  from  white  fly  is  generally  required, 
especially  when  the  purchaser  contemplates  planting  a  more  or  less 
isolated  grove. 

SUMMARY  OF  LOSSES. 

The  estimates  in  the  foregoing  pages  refer  to  ordinary  losses  where 
the  white  fly  is  unchecked  by  natural  enemies  or  by  artificial  methods 
of  control  and  not  to  exceptional  or  occasional  losses.  These  esti- 
mates, as  applying  to  the  fruit,  are  summarized  in  Table  III. 

Table  III. — Estimates  of  losses  to  orange  crops  by  white  fly  in  uncontrolled  condition. 


Ripening  retarded 

Number  ami  size  of  fruits 

Cost  of  cleaning 

Deterioration  in  shipping  quality 

Indirect  injury:  Increased  scale  and  disease  elTects  on  fruit. 
Loss  in  market  value 

Total 


Maximum. 

Minimum. 

Mean. 

Pir  cent. 

Per  ant. 

Per  cent. 

0 

2 

:U 

50 

20 

35 

10 

1 

5J 

G 

2 

4 

5 

1 

3 

in 

0 

0 

Mi 

26 

56 

24  WHITE    FLIES   INJURIOUS   TO   CITRUS    IN    FLORIDA. 

The  mean  of  the  total  percentage  of  estimated  loss  is  considered  by 
the  authors  to  represent  about  the  normal  loss  which  the  citrus  white 
fly  is  capable  of  causing  in  orange  groves.  It  is  estimated  that  the 
condition  is  reduced  to  about  45  per  cent  loss  in  the  average  infested 
grove  as  a  result  of  net  profits  from  spraying  with  contact  insecticides 
and  of  the  natural  efficiency  of  fungous  diseases. 

From  extensive  records  obtained  in  the  course  of  their  investiga- 
tions the  writers  estimate  that  the  citrus  white  fly  infests  at  present 
45  per  cent  of  the  citrus  groves  in  Florida.  Of  this,  5  per  cent  is  a 
sufficient  allowance  to  represent  the  groves  so  recently  infested  that 
normal  abundance  of  the  pest  has  not  been  reached.  An  injury  of 
45  per  cent  in  40  per  cent  of  the  groves  is  equal  to  about  18  per  cent 
of  the  entire  value  of  the  crop  as  it  presumably  would  have  been  if 
the  white  fly  were  not  present. 

The  latest  Florida  citrus  crop  concerning  which  statistics  are  avail- 
able is  that  of  1 907-8. 1  The  orange  crop  for  that  season  is  valued 
at  |3, 835, 000.  With  an  estimated  total  loss  of  about  15  per  cent 
this  represents  85  per  cent  of  the  value  of  the  crop  if  not  affected  by 
the  white  fly.  Accordingly,  the  estimated  loss  in  Florida  is  calcu- 
lated to  have  been  about  $680,000  for  oranges  and  similarly  on  the 
basis  of  10  per  cent  loss  to  grapefruit  on  a  valuation  of  $469,700,  the 
percentage  of  infested  groves  the  same  as  in  the  case  of  the  orange 
groves,  a  loss  of  $16,700  is  estimated,  making  the  total  loss  in  valua- 
tion of  fruit  about  $696,700  for  the  crop  of  1907-8.  The  crop  of 
1908-9  was  doubtless  affected  to  the  extent  of  $750,000  by  the  citrus 
white  fly. 

At  present  the  spread  of  the  fly  into  uninfested  groves  is  undoubt- 
edly faster  than  at  the  rate  of  5  per  cent  new  infestations  per  year. 
Even  on  this  basis,  however,  the  annual  increase  in  depreciation  in  the 
value  of  Florida  citrus  groves  due  to  white-fly  infestation  is  more  than 
$200,000  per  year.2  In  addition,  the  citrus  nursery  business  in  Florida 
is  affected  to  an  extent  hard  to  estimate,  but  which  would  be  only 
nominally  represented  by  $50,000  per  year. 

Figures  are  not  available  which  would  allow  approximate  estimates 
to  be  made  of  the  damage  by  the  citrus  white  fly  in  the  Gulf  coast 
citrus-growing  sections  outside  of  Florida,  but  the  widespread  occur- 
rence of  the  white  fly  in  those  States  indicates  that  the  losses  are 
heavy. 

INCREASED  COST  OF  MAINTENANCE . 

The  items  of  expense  of  maintenance  principally  affected  by  the 
white  fly    are   fertilization,    spraying,    and   fumigation.     In   Florida 

1  Tenth  Biennial  Report  of  the  Commissioner  of  Agriculture  of  the  State  of  Florida. 

2  This  is  not  shown  by  actual  depreciation,  for  the  number  of  groves  coming  into 
bearing  for  the  first  time  each  year  more  than  covers  the  loss. 


'I'll  i:  01  i  ftl  B    WHIT1     ii.  \  :   I  »is  i  aiBUTION.  25 

ordinarily  the  expense  of  the  fertilizer  necessary  to  maintain  orange 
t  rees  in  good  productive  condition  varies  from  LO  to  20  cents  per  bos 
of  fruit  produced.  The  wide  range  given  is  larger)  due  to  differences 
in  soil  conditions.  Mr.  B.  0.  Painter,  in  response  to  an  inquiry  on 
the  subject,  writes  thai  citrus  trees  infested  with  white  fly  in  Ins 
opinion  require  at  least  i">  per  cent  Increase  in  fertilizer  for  best 
results  under  the  circumstances.  On  the  basis  of  cost  of  fertilizer 
amounting  to  LO  to  20  cents  per  box  and  an  increase  of  15  percent 
due  to  white  fly  infestation,  the  extra  expense  which  tnaj  be  charged 
as  white  fly  injury  amounts  to  l . 5  to  3  cents  per  box. 

Cost  of  control  measures  properly  chargeablt  to  increased  cost  of  main- 
tt  nana .  — Estimates  based  on  the  experience  of  the  writers  in  fumi- 
gating and  in  spraying  for  the  white  fly  give  the  range  in  expense  of 
the  former  method  of  control  as  5.5  to  14  cents  per  box  of  oranges 
produced,  and  of  t ho  latter  method  12.5  to  20  cents  per  box.  These 
estimates  refer  to  thorough  control,  with  the  result  that  production  is 
entirely  unaffected  by  the  white  fly.  The  minimum  estimate  on  the 
expense  of  fumigation  refers  to  groves  so  located  that  the  migrations 
of  adults  from  outside  groves  does  not  make  treatment  necessary  more 
than  once  in  two  years.  The  maximum  estimate  refers  to  conditions 
where  treatment  every  year  is  required  to  prevent  loss.  Increase  in 
production,  due  to  destruction  of  scale-insect  pests,  is  not  taken  into 
consideration.  In  the  estimates  of  expense  of  control  by  spraying 
the  minimum  estimate  refers  to  cases  where  three  applications  of  in- 
secticide per  year  have  resulted  in  satisfactoiy  control.  This  result 
can  be  attained  only  after  the  insect  has  been  brought  into  complete 
subjection,  such  as  referred  to  in  the  introductory  paragraph  of  the 
subject  of  artificial  control.  Insecticides  costing  more  than  1J  cents 
per  gallon  when  mixed  ready  for  application  have  not  been  taken 
into  consideration. 

DISTRIBUTION. 

As  has  been  shown  in  the  historical  review,  the  citrus  white-fly 
at  present  is  generally  distributed  in  North  America.  In  the  north- 
ern part  of  the  United  States  it  occurs  in  greenhouses,  and  in  the 
southern  part,  and  in  limited  districts  in  California,  it  occurs  on 
citrus,  China  trees,  privet,  cape  jessamines,  and  other  food  plants. 
In  the  present  publication  we  arc  concerned  only  with  the  distribu- 
tion of  the  species  in  the  citrus  fruit-growing  regions  of  the  United 

States. 

In  the  United  States. 

According  to  the  statistics  of  the  Florida  commissioner  of  agricul- 
ture, in  1905  there  were  17  counties  in  the  State  reporting  more 
than  5,000  bearing  citrus  fruit  trees.  In  all  but  two  of  these,  Dade 
and  St.  Lucie,  the  citrus  white  fly  {Aleyrodes  citri)  occurs  to  a  greater 


26 


WHITE    FLIES   INJURIOUS   TO   CITRUS   TN    FLORIDA. 


or  less  extent.  (See  fig.  1.)  The  17  counties  referred  to,  arranged  in 
order  of  the  number  of  bearing  citrus  trees,  is  as  follows:  Orange,  Lake, 
Volusia,  Polk,  Putnam,  Brevard,  Hillsboro,  De  Soto,  Lee,  Manatee, 
Dade,  Marion,  St.  Lucie,  Osceola,  Sumter,  St.  John,  and  Alachua. 
Palm  Beach  as  well  as  Dade  and  Monroe  Counties  are  infested  with  the 
cloudy-winged  white  fly,  as  hereafter  noted,  but  so  far  as  known  the 
citrus  white  fly  does  not  occur  there.  In  order  of  the  percentage  of 
groves  infested  the  foregoing  counties  which  are  known  to  be  infested 
would  be  arranged  about  in  the  following  order,  so  far  as  our  obser- 
vations and  records  show:  Marion,  Alachua,  St.  John,  Manatee, 
Orange,  Lee,  Volusia,  Polk,  Putnam,  Lake,  Hillsboro,  Sumter,  De 
Soto,  Osceola,  and  Brevard.  If  the  groves  infested  by  the  cloudy- 
winged  white-fly  only  were  also  taken  into  consideration,  Hillsboro 

and  Lake  Counties 
would  be  transposed 
in  the  list,  as  would 
Osceola  and  Brevard, 
but  aside  from  this 
there  would  be  no 
change.  The  arrange- 
ment is  only  approxi- 
mate, being  based  on 
observations  made 
by  the  various  men 
connected  with  the 
white-fly  investiga- 
tions upon  informa- 
tion and  samples  of 
infested  leaves  re- 
ceived from  corre- 
spondents and  upon 
nearly  250  replies  received  in  response  to  circular  letters  sent  out  in 
the  spring  of  1907. 

At  the  present  time  the  writers  estimate  that  throughout  the  State 
of  Florida  about  40  per  cent  of  the  citrus  groves  are  infested  by  the 
citrus  white  fly,  and  that  an  additional  5  (or  10)  per  cent  are  infested 
by  the  cloudy- winged  white  fly  alone. 

The  citrus  white  fly  occurs  in  nearly  all  the  larger  towns  in  north- 
ern Florida,  infesting  the  various  food  plants  which  are  grown  as 
ornamentals  as  well  as  the  citrus  fruit  trees  which  are  grown  to  a 
limited  extent.  The  insect  is  of  common  occurrence,  principally  on 
China  trees,  cape  jessamines,  and  on  privet  and  hedges  of  Citrus 
trifoliata  in  South  Carolina  and  in  southern  Georgia,  Alabama,  Mis- 
sissippi, Louisiana,  and  Texas.  In  the  last  two  States  citrus  fruits 
are  being  grown  quite  extensively,  and  a  large  percentage  of  the 
citrus-growing  localities  are  infested. 


Fig.  l. 


-Map  showing  distribution  of  the  citrus  white  fly  (Aleyrodes 
citri)  in  Florida.     (Original.) 


"I  ii  i.   ci  ratU8    wini  i     i i\  :    DISl  » : 1 1 : i    i  [ON.  27 

Aside  from  the  Gulf  coast  States,  citrus  Fruits  in  the  United  Sti 
are  grown  onlj  in  California  and  Arizona.     The  citrus  white  fl\  does 
noi  occiii-  iii  Arizona.     In  California  the  pesl  was  first  discovered  in 
May,  1907.     Mr.  C.  L.  Marlatf   has  given  the  following  account  of 
the  distribution  ol'  the  white  lly  in  that  State  in  L907:1 

liarysville  La  situated  a  i'«'\v  miles  north  oi  Sacramento,  and  the  first  infestation 
seemed  limited  to  this  town,  but  toward  the  end  of  the  summer  the  white  fly  was 
discovered  well  established  at  Oroville,  in  Butte  County,  some  26  miles  to  the  north 
of  Marysville.  The  Marysville  infestation  was  confined  to  the  town  and  to  yard 
or  small  garden  orchards.  Oroville  lies  in  a  considerable  orange  district,  and  the 
white  fly  had  been  carried  from  the  town  into  several  of  the  adjacent  orchards  and 
had  become  rather  widely  scattered.  Shortly  after  the  discovery  of  the  fly  at  Marya- 
ville  it  was  found  also  to  have  established  itself  locally  near  Bakersfield,2  in  the  south- 
ern end  of  ilif  San  Joaquin  Valley,  and  separated  only  by  a  mountain  range  from  the 
citrus  districts  of  southern  California. 

In   Foreign  Countries. 

For  years  the  citrus  white  fly  has  been  supposed  to  be  an  intro- 
duced species,  and  much  interest  has  been  attached  to  its  occurrence 
elsewhere  than  in  North  America.  Prof.  H.  A.  Gossard  in  1903 
stated  that  Mr.  Alexander  (raw,  of  the  California  State  commission 
of  horticulture,  had  received  this  species  on  plants  from  Chile,  when' 
it  was  reported  to  be  a  great  pest.  Mr.  G.  W.  Kirkaldy,  in  his  cata- 
logue of  the  Aleyrodklse,  in  1907,  gives  "Mexico,  Brazil,  and  Chile 
(?)"  as  the  known  habitats  of  the  citrus  white  fly  outside  of  the 
United  States.  The  writers  are  informed  by  Prof.  A.  L.  Quaintance 
that  he  was  told  in  person  by  the  late  Prof.  Rivera,  of  Santiago, 
Chile,  that  the  citrus  white  fly  was  abundant  in  that  country.  Prof. 
Carlos  Camacho,  chief  vegetable  pathologist  at  Santiago,  Chile,  is 
also,  according  to  Prof.  Quaintance,  authority  for  the  statement  that 
it  occurs  there. 

The  Bureau  of  Entomology  received,  in  1906,  specimens  of  an 
aleyrodid  on  orange  leaves  from  China  which  Prof.  Quaintance 
determined  as  Aleyrodes  citri?  and  still  more  recently  it  received, 
through  Mr.  August  Mayer,  in  charge  of  plant-introduction  garden, 
and  through  the  California  state  commission  of  horticulture,  speci- 
mens of  orange  leaves  infested  with  what  Prof.  Quaintance  has 
identified  as  this  species  from  different  parts  of  China  and  Japan. 

The  occurrence  of  the  citrus  white  fly  in  India  (northwestern  Hima- 
layas) has  recently  been  established  by  Prof.  Quaintance,  who  has 
compared  Maskell's  A.  aurantii,  collected  in   the  region  mentioned 

1  Proceedings  of  the  Entomological  Society  of  Washington,  vol.  9,  pp.  121-122, 
1908. 

2  Specimens  of  the  species  present  at  r.akorsfield  were  examined  by  the  senior 
author  at  the  California  Stale  Insectary  at  Sacramento  and  found  to  be  the  cloudy- 
winged  white  fly  (A.  nubifera). 

3  Proceedings  of  the  Entomological  Society  of  Washington,  vol.  S,  Nos.  3-4,  p.  107. 


28  WHITE   FLIES   INJURIOUS   TO   CITRUS   IN    FLORIDA. 

above,  with  A.  citri,  and  failing  to  find  any  differences  in  the  egg  and 
pupal  stages  found  it  necessary  to  regard  the  name  given  by  Maskell 
as  a  synonym  of  that  given  by  Riley  and  Howard. 

The  citrus  white  fly  does  not  occur  in  Cuba,  so  far  as  known, 
although  it  is  not  unlikely  to  be  found  there,  since  there  have  been 
heavy  shipments  of  nursery  stock  from  infested  citrus  nurseries  in 
Florida  to  that  country  during  the  last  few  years. 

FOOD   PLANTS. 

AUTHENTIC    AND    QUESTIONABLE    RECORDS. 

The  separation  as  distinct  species  of  two  forms  formerly  considered 
as  belonging  to  the  species  Aleyrodes  citri  makes  it  necessary  that 
all  of  the  reported  food  plants  of  the  citrus  white  fly  be  verified. 
Nearly  60  species  of  the  genus  Aleyrodes  have  been  recorded  for 
North  America.  Of  these  less  than  20  have  been  described  in  the 
first  larval  stage  in  a  manner  which  distinguishes  them,  although 
when  carefully  studied  this  stage  has  been  found  to  have  striking 
specific  characters.  The  second  and  third  larval  stages  rarely  possess 
distinguishing  characters.  The  fourth  or  pupal  stage,  or  the  empty 
pupa  case,  is  used  as  the  basis  of  specific  descriptions  in  the  Aley- 
rodidae,  but  even  in  this  stage  a  careful  microscopic  examination  is 
usually  necessary  to  positively  determine  the  species.  Good  specific 
distinctions  in  the  adult  stage  have  been  found  only  in  a  few  species, 
and  even  those  entomologists  who  have  made  a  specialty  of  the  Alev- 
rodidse  do  not  attempt  to  distinguish  the  different  species  in  this 
stage.  It  is  obvious,  therefore,  that  a  list  of  food  plants  should 
properly  include  only  those  verified  by  entomologists,  with  determin- 
ations of  the  species  made  since  the  status  of  the  two  most  abundant 
citrus-infesting  species  of  Aleyrodes  has  been  fully  recognized.  Dr. 
E.  W.  Berger  has  recently  arranged  the  full  list  of  food  plants  and 
reported  food  plants  in  a  graphic  manner,  separating  the  list  into 
two  classes  according  to  the  degree  of  preference,  and  each  class  is 
subdivided  into  native  and  introduced  species.  This  method  of 
grouping  the  food  plants  is  here  adopted  (see  Table  IV)  with  the 
transposition  of  the  lilac  and  coffee  from  class  II  to  class  I  and  omit- 
ting certain  reported  food  plants  in  order  to  restrict  the  list  to  include 
only  positive  records,  leaving  the  others  for  a  separate  discussion. 
Dr.  Berger  has  recently  discovered  the  citrus  white  fly  on  wild  olive, 
and  has  also  verified  Prof.  Gossard's  report  of  the  citrus  white  fly  on 
Viburnum  nudum.  Both  of  these  food  plants,  together  with  the 
green  ash,  will  eventually  be  found  to  be  subject  to  heavy  infestation 
and  be  placed  in  class  I. 


Til  I     (I  rues    w  ii  ill     PLY!    FOOD    PLAN!  B.  29 

Tabi  i    1\       Definitely  known  food  plants  of  tin  citrus  whiU  Jly  i  Aleyrodu  i 

(    i   \-^    I       l'i;i  i  i  1:1;  I  D 

Introduced : 

1.  Citnu  (all  Bpeciee  cultivated  in  America 

■_'.  china  tree  (  Melia  ozedarach). 
:;.  [Jmbrella  China  tree  |  Melia  ozedarach  umbraculifer 
i.  Cape  jessamine  {Gardenia  jasminoid* 
.">.  Privets  (Ligttslrum  Bpp.  I. 
ii.  Japan  persimmon  (Diospyroshabi). 
7.  Lilac  {Syringa  s|>.  i. 
s.  Coffee    '  'offea  <ir<ihi,-<n. 
Native: 

9.    Prickly  ash  (Xanthoxylum  c/(ir(i-h>  rrulisi. 

10.  Wild  persimmon  {Diospyros  virginiana). 

(lass    11.   Occasionally    [NFESTED. 

Introduced : 

11.  Allamanda  {Allamanda  neriifolia). 

12.  Cultivated  pear  {Pyrus  spp.). 

13.  Banana  shrub  {Magnolia  fuscatu m  . 

14.  Pomegranate  {Punica  granatum). 
Native: 

15.  Smilax  (Smilax  sp.). 

16.  Cherry  laurel  {Prunus  laurocerasus) . 

17.  Wild  olive  or  devihvood  (Osmanthus  americanus). 

18.  Viburnum  (  Viburnum  nudum). 

19.  Green  ash  (Fraxinus  lanceolata). 

In  addition  to  those  in  the  foregoing  list  l  there  are  several  plants 
reported  as  food  plants  of  the  citrus  white  fly  which,  while  probably 
true  food  plants,  can  not  consistently  be  included  in  the  recognized 
list  until  the  observations  have  been  repeated  and  the  infesting  spe- 
cies positively  identified.  In  some  instances  where  eggs  or  larvae 
have  been  found  there  is  doubt  as  to  whether  the  white  fly  could 
develop  to  maturity  on  the  plants  in  question.  Plants  upon  which 
the  insect  is  unable  to  develop  to  maturity  can  not  properly  be  con- 
sidered true  food  plants.  The  following  is  the  list  of  plants  reported 
as  food  plants,  but  which  in  each  case  require  further  observations 
either  as  regards  the  ability  of  the  insect  to  reach  maturity  thereon 
or  as  regards  the  species  of  white  fly  concerned,  in  view  of  the  recent 
separation  of  A.  citri  and  A.  nubifera:  Water  oak,  reported  by  Prof. 
A.  L.  Quaintance;  Ficus  altissima,  Ficus  sp.  (from  Costa  Rica),  and 
scrub  palmetto,  reported  by  Prof.  H.  A.  Gossard;  honeysuckle  and 
blackberry,  reported  by  Dr.  E.  II.  Sellards;    oleander,  reported  by 

1  In  addition  to  those  already  mentioned  as  being  food  plants  in  Florida,  the  follow- 
ing plants  are  on  record  at  the  State  insectary  at  Sacramento,  Cal.,  as  food  plants  of  the 
citrus  white  fly  observed  at  Marysville  and  Oroville  by  agents  of  the  State  commission 
of  horticulture:  English  ivy  (Hedera  helix),  yellow  jessamine  (Jasminum  odoratissi- 
mum),  Ficus  macrophylla,  bay  (Laurus  nobilis),  tree  of  Heaven  {A ilanthus  glandulosa), 
and  crape  myrtle  (Myrtus  lagerstrcemia) .  Information  concerning  the  authorities  for 
the  plants  listed  is  not  available. 


30  WHITE    PLIES    INJUEIOUS   TO   CITRUS   IN    FLORIDA. 

the  senior  author  of  the  present  publication;  camellia,  reported  by 
Dr.  E.  W.  Berger.  Jii  the  case  of  the  last  two  plants  mentioned 
the  uncertainty  as  to  their  proper  standing  is  on  the  possibility  of 
the  insect  icaching  maturity  thereon  and  not  on  the  identity  of  the 
infesting  species. 

The  present  status  of  the  plants  which  have  heretofore  been  listed 
by  entomologists  as  food  plants  of  the  citrus  white  fly  is  shown  in 
the  foregoing  paragraphs.  There  are  doubtless  numerous  additional 
introduced  species  and  a  few  additional  native  species  of  plants  occur- 
ring in  the  United  States  which  serve  or  are  capable  of  serving  as 
food  plants  of  the  citrus  white  fly,  but  for  the  reasons  connected  with 
the  identification  of  the  insects,  stated  in  the  opening  paragraph  under 
the  subject  of  food  plants,  reports  of  food  plants  other  than  those 
included  in  classes  I  and  II  should  never  be  credited  unless  verified 
by  or  made  by  an  entomologist.  There  are  no  important  food  plants 
occurring  in  the  Gulf  coast  region  omitted  from  this  list,  and  future 
additions  to  the  list  probably  will  be  of  little  significance  economically 
as  affecting  the  control  of  the  pest.  There  is  a  widespread  belief  that 
many  other  common  trees,  shrubs,  and  vines  in  Florida  are  food  plants 
of  the  citrus  white  fly,  but  the  correctness  or  falsity  of  this  belief 
can  be  readily  ascertained  in  the  case  of  the  individual  plants  sus- 
pected by  submitting  specimens  of  the  foliage  and  of  the  infesting 
insect  to  the  Bureau  of  Entomology  or  to  the  State  experiment  station. 

There  are  three  common  causes  for  erroneous  reports  concerning 
citrus  white-fly  food  plants.  The  first  is  the  presence  of  sooty-  mold 
on  many  plants,  due  to  other  honeydew-secreting  insects,  such  as 
aphides,  scale  insects,  and  mealy  bugs.  The  insects  themselves  are 
not  seen  in  this  case  and  the  mistaken  idea  is  due  to  ignorance  of  the 
fact  that  other  insects  than  the  citrus  white  fly  excrete  honeydew  on 
which  the  same  species  of  sooty  mold  fungus  thrives.  The  second 
cause  for  erroneous  reports  in  this  respect  is  the  misidentification  of 
the  insect  concerned.  The  necessity  for  the  identification  of  the  in- 
festing insect  by  an  entomologist  has  been  discussed.  The  third 
cause  is  the  frequent  occurrence  of  the  adult  citrus  white  fly  on  the 
foliage  of  plants  upon  which  it  does  not  breed  and  upon  which  it  sel- 
dom or  never  deposits  an  egg.  In  the  course  of  the  present  investi- 
gation by  the  Bureau  of  Entomology  several  trees  and  shrubs  have 
been  thoroughly  tested  as  possible  food  plants  by  cage  experiments, 
and  observations  have  been  made  on  these  and  other  plants,  showing 
that  if  it  is  possible  for  the  citrus  white  fly  to  develop  on  one  of  them, 
it  is,  at  the  most,  of  too  rare  occurrence  to  be  of  any  significance. 
Cage  tests  have  been  made  with  oak  (Quercus  brevifolia),  Magnolia 
(Magnolia  foztida),  blackberry  (Rubus  spp.),  Laurel  cherry  or  mock 
olive  (Prunus  caroliniana) ,  and  cultivated  figs  (Ficus  carica)  and  crape 
myrtle  (Myrtus  lagertrozmia).     In  each  case  a  rearing  cage  (PI.  VII) 


Til  B   til  BUS    wiiiii     PLY:    FOOD    i'i  '.'<  1 

was  attached  i<>  the  end  of  a  branch  covering  ne^  growth  and  from 
.Mi  to  LOO  adults  of  .1.  citri  were  confined  tlierein.     Except  in  the 
{){'  the  blackberry,  in  winch  no  observation  was  made  on  the  point, 
the  adults  were  noted  as  resting  contentedly  and  apparently  feedin 
thf  leaves  for  one  <>r  two  days  after  being  confined.     In  ever)  « 
however,  ;ill  the  adults  were  dead  on  the  fourth  day  after  confinement 
on  tlif  plants  noted,  although  check  lots  of  adults  collected  ;ii  the  same 
time  l)ii t  confined  on  branches  of  citrus  trees  lived  for  a  norma]  period. 
No  eggs  were  deposited  in  any  of  the  tests,  although  the  check  lots 
deposited  eggs  on  the  citrus  leaves  in  a  normal  manner. 

Bach  of  the  five  plants  tested  with  the  cage  experiments  have  in 
addition  been  subjected  to  very  careful  examinations  by  the  writers 
under  such  circumstances  that  the  opportunities  for  infestation  by 
the  citrus  white  fly  were  at  their  best.  In  addition,  particular  atten- 
tion has  been  given  to  examinations  of  species  of  oaks  (Quercus  spp.) 
and  bays  (Persea  spp.),  guavas  (PsMium  spp.)  and  mulberries  ( Moms 
spp.),  when  located  near,  and  in  some  cases  with  branches  intermin- 
gling with  infested  citrus  or  other  favorite  food  plants. 

Economic  Significance  of  Food  Plants,  and  Interrelationship  Between  Food 

Plants  and  Insects. 

Entomologists  familiar  with  the  present  white-fly  situation  agree 
in  their  conclusion  that  a  requisite  for  satisfactory  control  of  this 
pest  is  proper  attention  to  food  plants  other  than  citrus  fruit  trees. 
Mr.  H.  G.  Hubbard,  who  was  a  well-known  authority  on  orange 
insects,  being  a  special  agent  of  the  Bureau  of  Entomology,  was  a 
strong  advocate  of  destroying  food  plants  of  the  white  fly  that  were 
of  no  value.  Dr.  Sellards,  formerly  entomologist  at  the  Florida  Ex- 
periment Station,  Dr.  Berger,  the  present  entomologist,  Prof.  P.  II. 
Rolfs,  director  of  the  Florida  Experiment  Station,  and  the  authors 
have  each  emphasized  the  importance  of  the  relation  of  the  various 
food  plants  to  white-fly  control. 

The  following  paragraph  from  -the  senior  author's  bulletin  on  the 
subject  of  fumigation  for  the  citrus  white  fly  1  states  in  a  general  way 
the  situation  in  this  respect  as  viewed  by  entomologists  who  have 
investigated  the  white  fly: 

The  presence  of  food  plants  of  the  white  fly  other  than  citrus  trees,  in  citrus  fruit- 
growing sections,  constitutes  a  serious  menace  and  in  itself  often  prevents  successful 
results  from  remedial  work.  Fortunately  the  list  of  food  plants  is  limited,  and  the 
greater  number  of  those  thus  far  recorded  is  subject  to  infestation  only  when  located 
near  or  in  the  midst  of  heavily  infested  citrus  groves.  The  food  plants  which  are  of 
most  importance  in  connection  with  the  white-fly  control  are  the  chinaberry  tiers. 
privets,  and  cape  jessamine,  and  these — except  for  the  last,  in  certain  sections  where 
grown  for  commercial  purposes — can  be  eradicated  readily,  or  their  infestation  may 
be  prevented  where  community  interests  precede  those  of  the  individual  in  controlling 


bulletin  76,  Bureau  of  Entomology,  U.  S.  Department  of  Agriculture,  pp.  9-10. 


32  WHITE   FLIES   INJURIOUS   TO   CITRUS   IN    FLORIDA. 

public  sentiment.  These  food  plants  favor  the  rapid  dissemination  of  the  white  fly 
from  centers  of  infest  at  ion  and  their  successful  establishment  in  uninfested  localities. 
They  seriously  interfere  with  the  success  of  fumigation,  as  well  as  of  all  other  remedial 
measures,  by  furnishing  a  favored  breeding  place  where  the  white  fly  can  regain 
its  usual  abundance  in  a  much  shorter  time  than  would  be  the  case  if  it  were  entirely 
dependent  upon  citrus  fruit  trees  for  its  food  supply.  The  plants  mentioned,  together 
with  Citrus  (rifoliata  (except  where  used  in  nurseries),  and  all  abandoned  and  useless 
citrus  trees  should  be  condemned  as  public  nuisances  and  destroyed  in  all  communi- 
ties where  citrus  fruit  growing  is  an  important  industry. 

Not  only  is  a  knowledge  of  the  relation  of  the  various  noncitrus 
food  plants  to  white-fly  injury  of  great  importance,  but  it  is  also  of 
considerable  importance  to  growers  to  know  the  capability  of  the 
insect  for  multiplying  on  the  different  citrus  fruit  trees  in  order  that 
advantage  may  be  taken  of  it  in  the  arrangement  of  new  groves  and 
the  improvement  of  old  groves. 

CITRUS. 

It  is  a  matter  of  common  observation  that  injury  from  the  white 
fly  is  most  marked  on  citrus  fruits  of  the  Mandarin  group.  This 
group  includes  the  Tangerine,  Satsuma,  and  King  of  Siam.  The 
sweet  oranges  are  next  to  the  mandarins  in  this  respect,  followed  by 
the  kumquats  and  grapefruits. 

The  relatively  less  injury  to  grapefruit  by  the  citrus  white  fly 
(A.  citri)  is  sometimes  obscured  by  the  presence  of  A.  nubifera. 
Blackening  of  foliage  and  fruit  by  the  citrus  white  fly  is  more  notice- 
able on  grapefruit  trees  when  they  are  surrounded  by  or  are  otherwise 
unfavorably  located  in  respect  to  oranges  or  tangerines.  Solid 
blocks  of  grapefruit  trees  rarely  show  more  than  slight  effects  of 
white-fly  infestation  when  only  the  citrus  white  fly  is  present.  An 
example  of  this  is  the  Manavista  Grove  at  Manavista,  Manatee 
County,  Fla.  This  grove  consists  of  22,000  grapefruit  trees,  and 
appreciable  blackening  of  the  foliage  is  rarely  seen  except  occasionally 
where  orange  groves  adjoin.  Only  one  record,  based  on  actual 
examination  of  leaves,  illustrating"  the  difference  in  the  degree  of 
infestation  of  adjoining  blocks  of  grapefruit  and  orange  trees  is 
available.  The  grapefruit  block  consisted  of  about  400  trees  located 
immediately  north  of  a  block  of  200  or  300  orange  trees  and  separated 
on  the  west  by  a  public  road  from  a  grove  of  about  800  orange  trees. 
On  April  23,  1909,  after  practically  all  the  overwintering  pupse  had 
matured,  an  examination  of  100  or  more  leaves  collected  at  random 
from  each  grove,  counting  the  pupa  cases,  showed  an  average  of  8 
insects  that  had  reached  maturity  on  the  grapefruit  leaves,  27  on 
the  orange  leaves  of  the  block  south,  and  56  on  the  orange  leaves  of 
the  block  west.  No  studies  have  been  made  to  determine  the  differ- 
ent degrees  of  susceptibility  to  white-fly  injury  among  the  different 
varieties  of  grapefruit,  but  the  Koyal  variety  appears  to  be  more 


Ill  B  CITRUS  WHIT!     PLY  :  FCH  ID    I'l.w  i 

nearly  immune  than  anj  other  of  those  commonly  groia  q.     Thi 
first  pointed  out  l>\  Mr.  K.  I).  Waite,  of  Palmetto,  Fla,     In  tin-  con 
aection   it   should   be  noted   thai    the   Royal   varietj    in   it>  general 
characteristics  is  not  a  typical  grapefruit. 

The  reason  lor  t  he  partial  immunity  of  grapefruit  trees  to  white  II \ 
injury  is  as  yet  obscure.  Several  observations  on  grapefruit  and 
orange  trees  growing  side  by  side  give  no  basis  for  the  supposition 
tli.it  it  is  a  matter  of  food-plant  preferences  of  the  adult  flies.  In 
some  cases  tin4  differences  in  the  amount  of  new  growth  must  be 
taken  into  consideration.  Counts  of  adults,  pupa  cases,  and  hatched 
eggs  of  tin1  citrus  whitefly  on  alternating  grapefruit  and  orange 
trees,  six  in  all,  located  on  the  laboratory  grounds  at  Orlando,  were 
made  on  dime  I,  L909,  when  no  new  growth  was  present  on  the  trees. 

The  Leaves  were  selected  at  random  and,  with  the  exception  of  a  few 
upon  which  adults  were  counted,  they  represented  the  spring  growth 
of  1909.  The  difference  between  the  number  of  the  adults  on  500 
grapefruit  and  500  orange  leaves,  87  and  104,  respectively,  is  not  as 
great  as  would  he  expected,  considering  the  much  greater  number 
of  insects  that  had  matured  on  the  orange  up  to  the  time  of  the  exam- 
ination. There  were  about  twenty  times  as  many  pupa  cases  on 
the  100  orange  leaves  as  on  the  100  grapefruit  leaves,  or  G  and  120, 
respectively.  This  was  offset  by  the  presence  of  about  three  times 
as  many  live  pupae  on  10  grapefruit  as  on  10  orange  leaves,  41  and  14, 
respectively,  making  the  sum  of  the  pupa  eases  and  live  pupae  4.16 
per  leaf  in  the  case  of  the  grapefruit  and  2.6  per  leaf  in  the  case  of  the 
orange.  This  is  about  the  same  proportion  as  the  number  of  hatched 
eggs  on  the  two  food  plants.  The  condition  of  the  leaves,  as  shown 
by  this  data,  fails  to  indicate  any  cause  for  the  partial  immunity  of 
grapefruit  trees. 

The  examinations  by  Mr.  W.  W.  Yothers  of  two  leaves  picked  at 
random  from  each  tree  in  a  small  isolated  grove  consisting  of  41 
grapefruit  and  28  tangerine  trees  gave  rather  striking  figures,  show- 
ing more  rapid  multiplication  of  the  citrus  white  fly  on  the  latter 
than  on  the  former.  The  first  examination  was  made  on  November 
4,  1908,  and  the  second  on  June  8,  1909.  On  the  former  date  the 
average  number  of  live  and  dead  white-fly  larvae  and  pupae  per  leaf 
was  31.9  on  the  grapefruit  and  96.2  on  the  tangerine,  16.6  and  80.9, 
respectively,  being  alive.  During  the  winter  a  series  of  fumigating 
experiments  reduced  the  numbers  of  the  wrhite  fly  so  that  at  the 
second  examination  the  number  per  leaf  was  1.1  on  the  grapefruit 
and  2.25  on  the  tangerine.  The  arrangement  of  the  two  kinds  of 
trees  in  the  grove  was  such  that  they  had  equal  chances  of  becoming 
reinfested  by  the  insects  which  escaped  the  effects  of  the  experimental 
tests. 

86850°— Bull.  92—11 3 


34  WHITE   FLIES   INJURIOUS   TO    CITRUS    IN    FLORIDA. 

The  difference  in  the  degree  of  injury  between  orange  and  tangerine 
trees  is  less  marked  than  between  tangerine  and  grapefruit  or  orange 
and  grapefruit,  but  the  difference  is  nevertheless  usually  quite  notice- 
able. The  practical  application  of  this  difference  in  the  degree  of 
adaptation  of  the  citrus  white  fly  to  the  various  citrus  food  plants 
will  be  discussed  in  a  forthcoming  bulletin  dealing  with  the  artificial 
control  of  the  white  fly. 

CHINA  TREES    AND    UMBRELLA    TREES. 

While  China  trees  (PI.  IV)  and  umbrella  China  trees  (PL  V),  when 
grown  for  shade  and  ornamental  purposes,  are,  as  has  been  pointed 
out,  very  injurious  to  citrus  fruit-growing  interests,  the  investigation 
of  the  utility  of  these  plants  as  trap  foods  gives  an  increased  import- 
ance to  a  definite  knowledge  concerning  them  as  citrus  white-fly  food 
plants.  Their  injuriousness  to  citrus  growers  is  very  clear  to  pro- 
fessional entomologists,  but  not  as  generally  appreciated  by  the  citrus 
growers  themselves  as  is  desirable. 

The  umbrella  tree  is  recognized  by  botanists  as  a  variety  of  the 
China  tree.  This  variety  is  the  one  most  commonly  grown  except 
in  a  few  localities,  and  observations  reported  herein  specifically  refer 
to  it  and  not  to  the  China  tree.  The  latter  tree  has,  however,  been 
under  observation  by  the  authors,  and  no  noticeable  difference  has 
been  observed  between  the  two  trees  in  their  relation  to  the  citrus 
white  fly,  and  the  data  and  observations  are  in  the  main  fully  as 
applicable  to  the  one  as  to  the  other. 

The  numbers  of  the  white  fly  which  mature  on  individual  umbrella 
trees  have  been  estimated  in  three  instances  and  found  to  range 
between  25,000,000  and  50,000,000  where  trees  are  favorably  located 
with  respect  to  nondeciduous  food  plants.  Examinations  were  made 
by  selecting  10  or  more  leaves  at  random  and  from  each  selecting 
a  leaflet  which  appeared  to  represent  the  average  condition  of  all 
the  leaflets  composing  the  leaf.  In  two  instances  it  was  found  that 
the  infestation  was  fully  as  great  toward  the  top  of  the  tree  as  on  the 
lower  parts.  In  one  instance  an  extensive  examination  of  different 
parts  of  an  infested  umbrella  tree  showed  a  decrease  from  lower 
branches  to  top  branches  of  50  per  cent.  In  order  to  be  fully  con- 
servative, this  percentage  has  been  used  as  the  basis  of  the  calcula- 
tions, making  the  average  infestation  throughout  the  tree  75  per 
cent  of  the  infestation  of  the  leaves  of  the  lower  branches.  Full- 
grown  leaves  were  found  to  consist  of  about  eighty-two  leaflets. 
Complete  records  were  made  of  eggs  and  of  live  and  dead  larvae  and 
pupse,  but  only  a  part  of  this  data  will  be  presented.  The  estimates 
and  counts  of  both  leaves  and  insects  in  the  case  of  the  first  tree  were 
made  by  the  senior  author;  in  the  cases  of  the  second  and  third  trees 
the  estimates  of  the  number  of  leaves  per  tree  represent  the  average 


■  cultur*. 


P 


m*:*i 


fe  Mj 


The  China  Tree. 

Fig.  1. — China  tree  defoliated  during  winter.    Fiur.  2. — Same  tree  in  full  foliage  in  summer. 

(Original.) 


iiuruau  of  Entomology!  U.  S 


Plate  V. 


Ul 


cc     Z 

CD      « 


I  II  l     «  I  I  in  s    WHITE    FLY:    FOOD    l 'I.  \ 


35 


of  three  estimates  one  bj  I  he  senior  author,  one  \>\  the  junior  author, 
and  one  l>\  Mr.  \Y.  \\ .  5  others.  The  counts  and  estimates-of  in 
were  made  l>\  the  senior  author  in  the  second  instance  and  bj  the 
junior  author  in  the  third.  The  data  obtained  in  these  examinations 
bearing  on  the  Dumber  of  insects  the  umbrella  trees  are  capable  of 
maturing  are  given  in  Table  V, 

l'\i;i  i    \       dumber  of  citrus  white  flies  developing  on  umbrella  China  trees. 


Date  of  exam- 
ination. 


1 

Oct. 

28,1 

•> 

^.ug. 

LQ 

L908 

a 

Au-. 

25 

L908 

Estimated 
Dumber  of 
leaves  on 

Hoc. 


•JO.  000 
25,000 
12,  000 


Number 
of  pupa 

per  leaf. 


Number 
of  li\  e 
pupae 

per  leaf. 


2,478 
1.910 
2,230 


Estimated 
number  of 
Insects  ma- 
tured on 

tree. 


I      49,560,000 
13.2     47 
4.0     26,760,000 


Estimated 
number  of 
larvae  and 
pupae  ali\  e 
ai  time  of 
examina- 
tion. 


82.000 

330.000 

58,800 


The  three  trees  examined  are  not  in  any  way  exceptional  as  regards 
the  degree  o(  infestation,  but  may  be  considered  as  representative  of 
the  condition  of  China  trees  and  umbrella  China  trees  in  localities 
where  the  citrus  white  fly  is  established.  Tree  No.  1  was  located  by 
the  roadside  near  a  5-acre  grove  of  newly  bearing  budded  orange  and 
grapefruit  trees  which  were4  lightly  infested  by  the  white  fly  and  on 
which  it  is  estimated  that  not  over  100,000  insects  could  have  matured 
on  any  one  tree  during  the  season.  Tree  Xo.  2  was  located  most 
unfavorably  for  a  heavy  infestation,  standing  in  a  vacant  lot  in  the 
business  section  of  Orlando  and  having  its  source  of  citrus  white-fly 
infestation  in  the  spring  almost  entirely  restricted  to  two  neglected 
and  worthless  orange  trees  of  small  size  growing  within  a  radius  of 
100  feet.  Tree  Xo.  3  was  located  in  front  of  the  laboratory  at 
Orlando,  with  36  orange  and  grapefruit  trees  on  the  grounds.  The 
least  conservative  of  the  authors'  estimates  would  place  the  number 
of  white  flies  which  matured  on  any  one  of  these  citrus  trees  during 
the  year  1908  as  not  over  500,000,  with  the  average  of  the  36  trees  at 
about  one-half  this  number.  It  is  estimated,  therefore,  that  the  one 
umbrella  tree  produced  upward  of  three  times  as  many  adult  citrus 
white  flies  during  the  year  1908  as  the  36  citrus  trees  on  the  labora- 
tory grounds  combined.  The  important  relation  of  the  remarkable 
multiplication  of  the  citrus  white  fly  on  China  and  umbrella  trees  to 
the  spread  of  the  pest  will  be  discussed  under  the  heading  "Spread." 

Two  new  points  of  importance  have  been  established  by  the  present 
investigations  in  regard  to  umbrella  China  trees  as  citrus  white  fly 
food  plants.  First,  this  insect  shows  in  one  respect  a  greater  degree 
of  adaptation  to  this  food  plant  than  to  citrus  plants,  as  shown  by 
the  very  low  rate  of  mortality  in  the  immature  stages.  Table  VI 
gives  the  data  obtained  by  five  counts  made  at  Orlando,  Fla.,  during 
these  investigations. 


36 


W  IIITE   FLIES   INJURIOUS   TO    CITRUS   IN    FLORIDA. 
Tablk  VI. — Mortality  of  citrus  white  fly  on  umbrella  China  tree  leaves. 


Date. 

Pupa 

Live 

larvae 

andpupae. 

Dead 

larvae 

andpupae. 

Mortality. 

Oct.  2s,  1906... 
July  8,  1908.... 
July  21,  1908... 
Aug.  19,  1908.. 
Aug.  25,  1908.. 

Total... 

MM, 

497 

113 
232 

312 

l 

256 
49  . 
169 

ill 
192 

51 
L52 

70 

Per  cent. 

12.0 
is. 7 
12.1 
3.-..  1 
13.4 

1.9G0 

813 

590 

L8.2 

The  record  made  on  August  19,  1908,  showing  the  highest  per- 
centage of  dead  stages  of  the  white  fly,  was  based  upon  10  leaflets 
selected  from  a  single  leaf  and  is  not  considered  so  typical  of  the  con- 
dition throughout  the  tree  examined  as  is  the  case  in  the  other 
records.  In  contrast  to  the  low  mortality  records  as  shown  by  the 
insect  forms  present  on  the  leaves  of  the  umbrella  trees,  26  records  of 
mortality  in  citrus  groves  gave  an  average  of  57.9  per  cent  dead  on 
the  leaves.  These  records  were  based  on  the  examination  of  about 
2,000  leaves  and  over  100,000  white-fly  forms.  It  should  be  noted 
that  the  mortality  in  the  above  records  is  based  on  the  number  of 
live  and  dead  larvae  and. pupa?,  and  of  pupa  cases  present  on  the 
leaves  at  the  times  of  the  examinations.  The  actual  mortality  would 
be  represented  by  the  difference  between  the  total  live  larva?,  live  pupae, 
and  pupa  cases  and  the  number  of  hatched  eggs.  On  umbrella  China 
tree  leaves  this  difference  is  slight  and  represented  for  the  most  part 
by  the  number  of  dead  larvge  and  pupae  found  on  the  leaves.  In  the 
case  of  the  citrus  trees,  on  the  other  hand,  the  number  of  citrus 
white-fly  forms  on  the  leaves  ordinarily  represents  only  from  25  to 
30  per  cent  of  the  total  number  of  eggs  deposited.  This  disappearance 
from  the  leaves  is  discussed  elsewhere.  Its  significance  in  this  con- 
nection is  that  the  actual  mortality  on  citrus  leaves  is  much  higher 
than  the  average  per  leaf  of  57.9  would  indicate.  The  citrus  white 
fly  forms  in  the  leaves  show  a  mortality  on  the  umbrella  tree  amount- 
ing to  only  one-third  of  the  mortality  on  citrus  trees.  The  considera- 
tion of  the  number  of  hatched  eggs  as  a  basis  for  mortality  estimates 
would  reduce  this  to  about  one-fifth.  The  figures  refer  to  citrus  groves 
where  the  citrus  white  fly  is  well  established.  In  newly  infested 
groves  the  rate  of  mortality  is  much  smaller  as  a  rule. 

The  second  important  point  established  in  the  course  of  the  investi- 
gations reported  herein  is  that  adult  citrus  white  flies  are  so  strongly 
attracted  by  growing  leaves  of  umbrella  trees  that  under  certain 
conditions  with  umbrella  and  citrus  trees  growing  side  by  side  more 
adults  collect  on  three  or  four  umbrella  leaves  than  are  present  on 
entire  citrus  trees  of  medium  size. 


Ill  I     CITRUS    w  II  III     ll  \  :    FOOD    IM.\  ' 


It  baa  hem  frequently  observed  thai  when  the  citrus  white  il\  Is 
first  becoming  established  in  a  grove,  if  China  trees  *or  umbrella  China 
ircc-  are  Dear,  adults  often  can  be  found  <>n  these  when  none  can  be 
Pound  on  surrounding  or  intervening  citrus  trees.  In  order  t<»  obtain 
;i  more  definite  idea  o\'  the  relative  attractiveness  of  umbrella  China 
trees  and  citrus  trees,  I  records  were  made  by  the  senior  author  on 
tln>  laboratory  grounds  (fig.  2)  ;ii  Orlando.  In  observation  No.  I,  the 
count   on  ci1  rus  \\  ;i^ 

tnadeon  Urees,viz,       0-0*/ING£,  ®  =  grape  fruit, 

,    .       ,    ,,      .,,  ,  1         •=  UMBRELLA    TREES; 

1  A.  I  B.  I  (  .  and  5       ~  r 

...  S  =  STORAGE  SHED,      L  =  LABORATORY. 

(  .  and  the  observa- 
tions on  umbrella 
China  trees  were 
small 


Wr 


ORANGE 
TREES 


made    on    i    smau  OR/1/VGE  TREES 

trees  located  about 
6  and  20  feet,  re- 
spectively, south- 
west i>\'  1  A.  These 
umbrella  China  trees 
were  slender  2-year- 
old  growths  about  4 
and  5  feet  high  and 
together  bearing 
about  40  leaves. 

Observation  No.  2 
was  made  on  grape- 
fruit and  orange 
trees  E  6,  E  5,  E  4, 
D  5,  D  4,  and  F  3 
and  two  stems  of 
the  umbrella  China 
tree  cluster  in  space 
F  7  nearest  to  tree 
E  6.  Observation 
No.  3  was  made  on 
tree  A  4  and  the 
nearest  umbrella  China  tree  sapling.  This  Latter  had  been  defoliated 
since  observation  No.  1  was  made.  Observation  No.  4  was  made  on 
citrus  trees  D  7,  E  6,  E  5,  E  4,  E  3,  and  F  3  and  on  two  stems  of 
the  umbrella  cluster  which  had  been  defoliated  since  observation 
No.  2.  The  data  obtained  by  the  four  observations  are  given  in 
Table  VII. 


// 

o    o          o    o 

/o 

-E 
9 

o          o                o 
o          o 

8 

o    o    o 

7 
6 

o          o    o         .#• 

o     o    o    o    o 

5 

®          o    ®    o 

4 

o    ®     o    o    o 

• 

3 
2 

/ 

•MP 

o    mVo     o    o 

1 

5 


/>      B     C     O    £    F 

Fir,.  2.— Diagram  of  the  laboratory  grounds  at  Orlando,  Fla. 
(Original.) 


38 


WHITE   FLIES   INJURIOUS    TO   CITRUS   IN    FLORIDA. 


Table  VII. — Relative  attractiveness  to  the  citrus  white  fly  of  foliage  of  umbrella  China 

trees  and  citrus  trees. 


Observer 
tion  No. 

Date. 

Citrus  trees.                          Umbrella  China-trees. 

Number 

of 
minutes. 

Number 

of  adults 
counted. 

Number    x-,,™k™. 
of  trees     Nu™ber 

Tned."     »*■»*« 

Number 

of  adults 
counted. 

Approx- 
imate 
number 
of  leaves 
exam- 
ined. 

1 

2.    . 

1909. 
May    18 

...do  .... 

5 
5 
3 
5 

257 
19 
34 
52 

4                   5 
6                  5 
1                   3 
6                   5 

508 
615 
477 
830 

25 

30 

6 

15 

3 

4 

June  11 
...do.... 

Total  . 

18 

362 

17                 18           2,427 

76 

In  all,  2,789  specimens  were  counted,  of  winch  88  per  cent  were  on 
umbrella  China  tree  leaves.  It  was  estimated  that  in  each  record  on 
a  citrus  tree  approximately  2,000  leaves  were  examined,  making 
34,000  in  all.  The  individual  leaflets  composing  the  76  umbrella- 
tree  leaves  numbered  approximately  6,000.  For  practical  purposes 
these  leaflets  are  more  comparable  to  the  citrus  leaves  although  the 
latter  have  on  the  average  fully  twice  as  much  surface.  With  this 
basis  for  comparison  it  can  be  figured  from  the  above  data  that  there 
was  about  one  adult  white  fly  per  100  leaves  on  the  citrus  trees  while 
there  were  about  40  adults  per  100  leaflets  on  the  umbrella  trees. 

As  has  been  indicated,  the  difference  between  the  number  of  China- 
tree  leaves  in  numbers  3  and  1  and  between  4  and  2,  respectively, 
represents  the  oldest  spring  growth,  which  was  removed  on  May  24, 
leaving  only  a  few  growing  leaves.  No  direct  comparison  was  made 
between  the  attractiveness  of  the  older  growth  of  citrus  and  umbrella 
trees  but  apparently  there  is  no  striking  difference  between  the  two 
food  plants  in  this  respect.  New  watershoots  were  present  on  the 
citrus  trees  on  both  dates  when  observations  were  made  but  only  in 
the  case  of  one  tree,  4  A,  were  many  adults  found  on  this  growth. 
In  observation  No.  1  on  the  tree  mentioned  (4  A)  200  adults  were 
counted  on  two  watershoots.  Except  for  watershoots  there  was  no 
new  growth  on  any  of  the  citrus  trees. 

At  Orlando  the  umbrella  trees  usually  start  to  put  on  new  foliage 
in  the  spring  before  new  growth  appears  on  citrus  trees.  As  a  con- 
sequence China  and  umbrella  trees  located  near  infested  citrus  trees 
receive  large  numbers  of  adults  of  the  citrus  white  fly  which  migrate 
in  search  of  attractive  food.  On  February  22,  1909,  the  authors 
noted  on  the  laboratory  grounds  that  the  shoots  of  the  umbrella  tree 
were  beginning  to  put  out  new  growth,  the  leaves  not  fully  unfolded. 
The  citrus  white  fly  was  found  scatteringly  on  the  umbrella  leaves 
but  on  citrus  trees  specimens  could  be  found  only  after  careful 
search. 


Till'   CITBUS    w  ii  i  i  i     PLY:    POOD    PLANTS.  39 

On  March  27,  1907,  near  the  laboratory  .  then  located  in  the  ■.  rove 

of  Me.  J.  M.  ( 'licnc\ .  a  st  riking  example  of  i  be  at  I  racl  n  eness  of  i  he 
umbrella  tree  was  observed.  The  tree  referred  t<>  was  about  25  feel 
high  and  tlic  leaves  which  were  <>n  the  average  onlj  about  half 
developed  were  estimated  to  number  5,000.  Ten  leaves  were 
selected  at  random  within  10  feet  <»!'  the  ground  and  the  number  of 
adults  and  eggs  was  counted,  the  former  numbering  5.3  per  leaf 
on  the  average  and  the  latter  160  per  leaf.  The  tree  was  cut  down 
and  an  examination  of  the  topmost  leaves  showed  an  average  of  is<> 
eggs  per  leaf;  the  adults,  being  disturbed,  were  not  counted,  but 
judging  from  the  number  <>f  eggs  present  they  evident  1\  were  more 
rather  than  less  numerous  than  on  leaves  near  the  ground.  Con- 
sidering the  average  of  5.3  per  leaf,  however,  the  total  number  of 
adults  on  the  tree  would  be  estimated  at  20, 500,  and  at  160  eggs  pet- 
leaf  the  number  of  eggs  deposited  would  be  estimated  at  800,000. 
At  the  time  of  this  observation  about  50  per  cent  of  the  insects  which 
overwintered  on  the  citrus  leaves  had  matured.  The  citrus  white 
lly  had  been  much  reduced  throughout  the  grove,  in  some  sections 
by  unexplained  influences,  in  others  by  these  influences  and  fumi- 
gation experiments  combined,  and  on  a  few  tangerine  trees  by  a 
fungus  parasite,  red  Aschersonia.  The  location  of  the  umbrella  tree 
did  not  seem  to  be  a  favorable  one  as  regards  opportunities  for 
white-fly  infestation,  but  examination  showed  the  infestation  to  be 
at  least  100  times  greater,  as  regards  the  number  of  adults  present, 
than  on  any  citrus  tree  in  the  grove.  There  were,  in  fact,  too  few  eggs 
deposited  on  the  leaves  of  the  citrus  trees  to  allow  of  sufficient  multi- 
plication of  the  white  fly  during  the  season  to  cause  any  blackening 
of  foliage  or  fruit. 

CAPE    JESSAMINE. 

The  cape  jessamine  has  long  been  recognized  not  only  as  a  favorite 
food  plant  of  the  citrus  white  lly,  but  as  especially  important  eco- 
nomically on  account  of  its  retaining  its  foliage  throughout  the  year. 
From  a  statement  by  Riley  and  Howard  !  concerning  observations 
by  Mr.  H.  G.  Hubbard  and  statements  by  Dr.  H.  J.  Webber,  Dr. 
Montgomery,  and  others  in  the  discussions  on  the  citrus  white  fly  at 
a  meeting  of  the  Florida  State  Horticultural  Society,2  it  appears  that 
the  freezes  of  December,  1904,  and  February,  1905,  wliich  completely 
defoliated  citrus  trees  when  not  especially  protected,  failed  to  defo- 
liate cape  jessamines.  In  many  localities  it  is  probable  that  tins  food 
plant  was  responsible  for  the  survival  of  the  white  fly  at  the  time 
referred  to.     According   to   Dr.  Sellards, 3  temperatures   as   low   as 

1  Insect  Life,  vol.  7,  p.  282. 

2  Proceedings  of  the  Florida  State  Horticultural  Society,  1896,  p.  78. 

3  Press  Bulletin  56,  Florida  Agricultural  Experiment  Station,  p.  2. 


40  WHITE   FLIES  INJURIOUS   TO   CITRUS   IN   FLORIDA. 

16°  above  zero  at  Lake  City,  between  January  26  and  January  29, 
1905,  failed  to  defoliate  cape  jessamine. 

Excepi  where  grown  for  commercial  purposes,  as  is  the  case  at 
Alvin,  Tex.,  where  the  blooms  are  sliipped  to  northern  markets,  or 
where  grown  in  nurseries,  cape  jessamines  have  not  been  observed 
growing  in  sufficient  abundance  to  materially  affect  near-by  citrus 
trees  in  sections  where  the  white  fly  is  already  established.  If  over- 
looked in  connection  with  the  fumigation  of  citrus  groves  or  defolia- 
tion of  citrus  trees 'by  cold,  cape  jessamines  might  become  a  serious 
hindrance  in  the  control  of  the  white  fly.  The  greatest  economic 
importance  of  the  cape  jessamine  as  a  food  plant  lies  in  the  great  dan- 
ger it  presents  as  a  distributer  of  the  white  fly.  Tliis  mil  be  referred 
to  again  under  the  subject  of  methods  of  spread. 

The  subject  of  the  adoption  of  the  cape  jessamine  by  the  citrus 
white  fly  is  not  of  sufficient  importance  to  have  been  given  more 
than  incidental  consideration.  In  general  the  degree  of  adoption 
seems  to  be  less  than  is  the  case  with  the  umbrella  and  China  trees. 
On  November  17,  1907,  an  examination  made  of  30  leaves  picked  at 
random  from  both  old  and  new  growTth  of  a  cape  jessamine  wdhch 
appeared  to  be  in  an  ordinary  condition  of  infestation  as  observed 
when  growing  near  infested  citrus  trees  showed  that  there  existed  an 
average  of  45.1  forms  per  leaf. 

The  extensive  growth  of  cape  jessamines,  or  gardenias,  as  the 
blooms  are  sometimes  called,  for  commercial  purposes  is  known  to 
the  authors  and  occasions  a  conflict  of  interests  only  in  Alvin,  Tex. 
From  the  orange  grower's  standpoint  this,  at  the  most,  applies  to  a 
location  adjoining  an  orange  grove  where  the  citrus  white  fly  is  uncon- 
trolled. Fortunately,  howrever,  for  the  citrus  growers,  it  is  of  great 
importance  to  the  success  of  the  florist's  business  that  the  white  fly 
be  kept  in  subjection  in  gardenias. 

PRIVET   HEDGES. 

Privet  hedges  are  not  uncommon  in  citrus-growing  sections,  and 
heavy  infestations  by  the  citrus  white  fly  occur  in  parts  of  Georgia 
and  South  Carolina,  where  no  citrus  trees  are  grown.  As  a  food 
plant  the  privets  are  of  economic  interest  in  the  same  respects  as  is 
the  cape  jessamine,  but  they  are  more  extensively  grown  and  of  pro- 
portionally greater  importance.  No  studies  have  been  made  of  the 
degree  of  adaptation  and  attractiveness,  but  the  several  species  of 
privet  observed  in  infested  localities  have  shown  the  propriety  of 
classing  them  with  citrus,  -China  trees,  umbrella  China  trees,  cape 
jessamine,  and  other  preferred  food  plants.  The  senior  author  ob- 
served a  migration  of  adults  from  privet  hedges  in  Victoria,  Tex.,  in 
the  summer  of  1904,  winch  indicated  that  a  hedge  of  this  material 


'I'll  I     I  i  I  1:1    3    w  m  i  i  i     PLY:    POOD    PLANTS.  I  1 

might  well  be  compared  in  Its  injurious  influence  on  citrus-growing 
Interests  bo  one  or  more  umbrella  or  China  trees.  The  privet,  like 
the  cape  jessamine,  is  hardy,  and  the  disadvantages  of  the  former  in 
this  connection  are  the  same  as  those  mentioned  in  discussing  the 
latter  Pood  plant. 

JAPANESE    A\i>    wiin    PERSIMMONS. 

Japanese  and  wild  persimmons  are  attractive  l<>  the  citrus  white 
fly  earlj  in  the  season,  but  appear  (<>  be  very  little  or  not  at  all  so 
late  in  the  season.     Being  deciduous,  their  economic  importance  as 

white  fly  food  plants  is  proportionally  small.  ruder  norma]  condi- 
tions the  Japanese  persimmons  appear  much  more  attractive  to  the 

citrus  white  fly  than  citrus  trees.  These  conditions  have  not  been 
investigated,  but  they  are  probably  dependent  upon  the  appearance 
of  new  growth  in  the  spring  a  little  earlier  on  persimmon  than  on 
citrus.  On  June  1(>,  L909,  an  examination  of  a  large  bearing  per- 
simmon tree  surrounded  by  citrus  nursery  trees  and  bearing  citrus 
trees  of  different  kinds  showed  that  the  first  spring  growth  of  the 
persimmon  was  much  more  attractive  to  the  first  brood  of  adults 
than  were  the  citrus  trees.  The  second  brood  of  adults,  however, 
found  the  persimmon  comparatively  unattractive  and  showed  a 
marked  preference  for  the  citrus  trees.  The  earliest  citrus  growth  of 
the  spring  had  become  fully  matured,  and  no  new  growth  appeared 
until  after  the  second  brood  of  adults  had  practically  disappeared. 
The  comparative  condition  of  infestation  is  shown  by  counts  made 
on  leaves  picked  at  random  from  the  persimmon  tree  and  from  the 
surrounding  citrus  trees,  including  the  sweet  orange,  sour  orange, 
tangerine,  and  grapefruit.  The  average  infestation  with  first- 
generation  forms  of  the  citrus  white  fly  on  25  leaves  each  of  per- 
simmon and  citrus  was  in  the  ratio  of  10.9  to  1.3,  while  that  of  the 
same  number  of  leaves  by  the  second  generation  was  in  the  ratio  of 
no  forms  on  the  persimmon  leaves  as  compared  with  191  on  the  citrus, 
thus  showing  the  great  preference  of  the  second  generation  of  adults 
for  citrus  growth. 

Neither  the  Japanese  nor  the  wild  persimmons  are  usually  infested 
by  the  citrus  white  fly  to  the  extent  of  causing  noticeable  blackening 
from  sooty  mold.  The  infestation,  however,  might  be  between  from 
five  to  ten  times  as  great  as  on  the  leaves  from  the  trees  referred  to  above 
without  producing  this  result.  Small  wild  persimmon  bushes  have 
been  observed  in  a  growing  condition  at  the  time  the  adults  of  the  sec- 
ond brood  are  on  the  wing,  and  at  such  times  they  sometimes  appear  to 
be  very  attractive  as  food  plants.  Mr.  W.  W.  Yothers  has  observed 
near  Hawthorn.  Fla.,  on  April  29,  1909.  the  citrus  white  fly  on  wild 
persimmon  bushes  growing  in  pine  woods  at  distances  upward  to  one- 


42  WHITE    FLIES    [NJTJBIOUS   TO   CITRUS   IN   FLORIDA. 

fourth  of  a  mile  from  any  citrus  grove,  and  the  junior  author  has 
made  similar  observations  along  roadsides  near  Orlando,  Fla.,  in 
June,  1909,  the  insects  being  in  the  adult  stage  only  in  this  latter 
case.  On  the  other  hand,  the  senior  author  noted  on  June  IS,  1909, 
that  wild  persimmon  bushes  growing  in  a  vacant  lot  with  China  trees 
and  abandoned  citrus  trees  were  only  very  slightly  infested,  although 
the  citrus  trees  and  the  China  trees  were  heavily  infested.  The 
wild  persimmon  had  made  vigorous  growth,  but  its  white-fly  infesta- 
tion consisted  of  less  than  100  eggs  per  leaf  and  an  occasional  adult. 
The  examination  of  leaves  of  the  China  tree  showed  hundreds  of 
pupae  and  pupa  cases  per  leaf,  with  a  few  adults  and  newly  deposited 
eggs.  The  old  citrus  leaves  bore  many  larva3,  pupa3,  and  pupa 
ca^es,  and  the  new  leaves  bore  hundreds  of  unhatched  eggs.  The  wild 
persimmon  bush  was  as  favorably  located  with  respect  to  citrus  trees 
as  was  the  China  tree.  Notwithstanding  the  exceptions  noted  in 
degree  of  attractiveness,  the  Japanese  and  the  wild  persimmons  very 
evidently  rank  well  below  citrus  trees,  China  trees,  and  umbrella 
China  trees. 

In  so  far  as  observed  the  persimmons  have  little  effect  on  the  con- 
trol of  the  citrus  white  fly,  but  in  special  cases  they  may  rank  as 
important  food  plants.  The  fact  that  the  Japanese  persimmon  is  a 
producer  of  fruit  of  some  commercial  value  makes  its  ordinary  light- 
ness  of  infestation  a  matter  of  gratification.  The  wild  persimmon,  on 
the  other  hand,  is  of  practically  no  value  either  for  shade  or  fruit,  and 
can  easilv  be  destroyed  where  advisable. 


lilac  is  not  commonly  grown  in  the  citrus-growing  regions  of  t he- 
Gulf  States,  and  on  this  account,  so  far  as  observed,  presents  no 
element  of  menace  to  orange  groves.  In  company  with  all  of  the 
ornamental  plants  listed  as  preferred  food  plants  this  one  must  be 
considered,  however,  as  undesirable  for  introduction  and  growing 
hi  citrus-growing  regions. 

PRICKLY  ASH. 

Belonging  to  the  family  Rutaceae,  to  which  the  genus  Citrus  also 
belongs,  it  is  not  strange  that  the  prickly  ash  is  a  favorite  food  plant 
of  the  citrus  white  fly.  This  plant  seems  to  be  highly  attractive  to 
the  adult  flies,  frequently  being  observed  infested  with  more  adults 
than  many  near-by  citrus  trees  combined.  The  prickly  ash  is  common 
in  Florida  and  in  some  localities,  where  growing  in  abundance  along 
roadsides,  it  constitutes  a  distinct  menace  to  citrus  groves  through  its 
connection  with  the  spread  of  the  white  fly  from  city  and  town  to 
country  and  from  grove  to  grove. 


fHE  CITRUS  WHITE  PLY  I  SPREAD.  1 ! 3 


Dr.  E.  W.  Berger  has  reported  having  observed  a  coffee  tree  thor- 
oughly infested  with  as  many  eggs  on  its  leaves  as  citrus  leaves  may 
have.  This  \\n)<\  plant  is  too  rarely  grown  in  the  Gulf  States  in 
orange-growing  regions  to  be  of  any  importance  economically  b  b 
w  hite-fly  food  plant . 

OC<   LSIONALL1    [NFBBTED    POOD    PLANTS. 

The  plants  listed  in  Class  1 1  as  a  \\  hole  are  of  very  litt  le  importance 
as  regards  their"  bearing  on  white-fly  control.  Banana  Bhrub,  cherry 
lame!,  and  cultivated  pear  mighl  well  !>e  considered  in  a  third  class 
for  rarely  infested  plants.  Although  not  uncommon,  their  attraction 
for  the  citrus  while  fly  is  so  slight  as  to  make  it  safe  to  ignore  them 
except  in  the  matter  of  introducing  the  fly  on  them  into  uoninfested 
districts.  In  unpublished  notes  Dr.  Berger  lias  recorded  the  wild 
olive  as  a  food  plant.  He  has  observed  the  wild  olive  infested  in  com- 
paratively isolated  places.  The  junior  author  has  observed  wild  olive 
heavily  infested  in  Charleston,  S.  (\,  and  in  several  places  in  Orange 
County,  Fla.  The  wild  olive,  being  an  evergreen,  if  neglected  may 
prove  to  be  of  considerable  importance  as  a  food  plant  when  growing 
in  abundance  near  a  fumigated  grove  or  when  citrus  trees  have  been 
defoliated  by  cold. 

Dr.  Berger  has  recorded  pomegranate,  allamanda,  and  smilax  as 
food  plants,  and  has  verified  Prof.  GossaroVs  record  of  Viburnum 
nudum  as  a  food  plant  of  the  citrus  white  fly.  The  positions  of 
these  plants  as  regards  their  attractiveness  to  the  citrus  white  fly  has 
not  been  fully  determined,  and  further  observations  will  perhaps 
show  one  or  more  of  them  to  be  of  fully  as  high  if  not  of  higher  rank  in 
this  respect  than  the  persimmons.  In  general,  however,  like  the  coffee 
and  lilac  of  Class  I,  they  are  not  of  sufficiently  common  occurrence  in 
the  Gulf  coast  citrus-growing  regions  to  be  of  much  economic  impor- 
tance as  citrus  white-fly  food  plants. 

SPREAD    IX    THE    UNITED    STATES. 

There  is  seldom  positive  evidence  in  regard  to  the  means  by  which 
the  citrus  white  fly  has  become  established  in  a  previously  non- 
infested  grove  or  locality.  Such  direct  observations,  however,  as  it  is 
possible  to  make,  aided  by  strong  circumstantial  evidence,  give  us  a 
sufficient  knowledge  of  the  methods  of  spread  to  show  the  advisa- 
bility of  certain  restrictive  measures. 

Checks  on  Successful  Establishments. 

Fortunately  the  chances  are  greatly  against  the  successful  estab- 
lishment of  the  citrus  white  fly  in  a  previously  uninfested  locality, 
which  is  outside  the  limits  affected  by  large  numbers  of  migrating 


44  WHITE    FLIES   INJURIOUS   TO   CITRUS   IK    FLORIDA. 

adults.  If  this  were  not  so  the  pest  would  have  become  established 
in  every  grove  of  the  State  long  before  the  present  time.  Except  for 
spread  by  direct  flight  and  on  nursery  trees  and  ornamental  plants, 
the  chances  are  against  more  than  a  few  insects  being  introduced  into 
a  particular  grove  by  any  of  the  other  methods  discussed  hereafter. 

In  the  case  of  a  single  adult  there  are  two  chances  in  three  that  it 
would  be  of  the.  reproductive  sex.  If,  as  would  be  probable,  the 
specimen  were  a  female,  there  would  be  about  one  chance  in  three 
that  it  would  not  have  been  fertilized.  In  this  case  the  second 
generation  of  adults  would  all  be  males,  as  shown  by  the  observations 
recorded  under  the  subject  of  Parthenogenesis.  This  would,  of  course, 
end  the  infestation  directly  due  to  the  single  specimen  introduced, 
as  the  original  female  would  have  died  several  weeks  before  the  first 
male  matured.  In  case  the  originally  introduced  specimen  were  a 
female  and  fertile  the  chances  of  a  male  appearing  among  the  second 
generation  are  not  definitely  known,  but  are  with  little  doubt  only 
small.  The  chances  of  such  a  male  appearing  at  a  favorable  time  to 
meet  with  and  to  fertilize  a  female  of  the  same  parentage  are  practi- 
cally negligible,  though  possible  as  a  result  of  the  great  variation  in  the 
length  of  the  life  cycle  as  recorded  under  life  history.  The  third 
generation  would,  therefore,  in  all  probability,  be  all  males,  and  the 
infestation  ended.  The  chances  that  a  single  adult  specimen  intro- 
duced into  an  isolated  grove  or  into  a  previously  noninfested  com- 
munity would  successfully  establish  a  permanent  infestation  are 
extremely  small.  The  chances  are  only  slightly  increased  by  an 
increase  to  5  or  even  10  in  the  number  of  adults  originally  introduced 
into  a  single  grove. 

From  the  foregoing  considerations  it  is  evident  that  two  or  more 
distinct  introductions  of  even  a  few  individuals  at  proper  intervals 
during  a  single  season  might  greatly  increase  the  chances  for  the  suc- 
cessful establishment  of  the  pest. 

Flight  of  Adults. 

The  flight  of  adults  is  the  most  important  method  of  local  distribu- 
tion and  is  also  an  important  element  in  its  association  with  spread  by 
means  of  winds  and  vehicles,  railroad  trains,  and  boats. 

The  distance  to  which  the  insect  is  capable  of  flying. — It  would  be 
almost  impossible  to  obtain  positive  records  on  the  distance  the  adult 
citrus  white  fly  is  capable  of  flying.  Mr.  W.  W.  Yothers,  on  April  29, 
1908,  found  on  wild  persimmon  first  and  second  generations  of  this 
species  of  fly  at  a  distance  of  one-fourth  of  a  mile  from  the  nearest 
orange  grove,  which  was  also  the  nearest  point  of  the  occurrence  of  a 
food  plant  upon  which  the  insect  could  have  passed  the  winter.  The 
infested  persimmons  were  in  pine  woods  and  the  insects  were  in  such 
numbers  that  it  was  evident  that  spread  through  pine  woods  might 


Til  E  CITRUS  W HIT!     FLY!      PR]  ID.  1 5 

easily  greatly  exceed  one  fourth  <»f  b  mile.  Mr.  \\ .  C.  Tempi 
Winter  Park,  Fla.,  states  thai  be  has  observed  adults  migrating  into 
one  of  his  groves  <>n  Lake  Ma  it  land  under  circumstances  plainly  indi- 
cating thai  they  bad  traveled  over  the  water  for  IJ  miles.  Dr. 
Berger  has  recorded  an  instance  which  presents  strong  evidence  that 
adult  white  flies  have  heavilj  infested  citrus  trees  through  flights  of  ;i 
mile  or  more.  On  the  other  hand,  there  are  orange  grpves  within 
three  fourths  of  a  mil**  of  the  city  limits  of  Orlando,  Pla.,  and  within 
2  miles  of  I  he  court  house  which  have  only  so  recent  ly  become  infest  ed 
that  no  blackening  of  the  foliage  has  taken  place,  although  the  citrus 
white  fly  has  occurred  at  Orlando  for  more  than  lo  years  with  migrat- 
ing adults  m  sunimer  about  as  abundant  as  in  any  town  iii  the  State. 
As  regards  the  capability  of  flight  of  the  citrus  white  fly,  it  may  be 
said  to  be  undoubtedly  more  than  a  mile  and  perhaps  several  miles 
when  aided  by  a  gentle  breeze.  Distances  of  even  a.  mile,  however, 
are  not  usually  attained  except  under  certain  circumstances  which 
are  largely  preventable  and  which  are  discussed  in  the  following 
paragraph. 

Cause  of  extensive  migrations  by  flight. — Overpopulation  of  food 
plants,  usually  associated  with  the  emergence  of  adults  in  large  num- 
bers a l  seasons  when  the  new  and  attractive  growth  is  scarce  or  en- 
tirely wanting,  is  the  main  cause  for  migrations  from  citrus,  cape 
jessamine,  and  privet.  Migrations  from  China  trees  and  umbrella 
trees,  probably  the  most  potent  factors  in  the  spread  of  the  pest,  are 
not  due  directly  to  overpopulation,  so  far  as  observed,  since  leaves  are 
never  overcrowded  in  a  manner  comparable  to  the  overcrowding 
on  citrus  leaves.  An  average  of  25  live  larvae  or  pupae  and  pupa 
cases  per  square  inch  of  lower  leaf  surface  would  represent  an  un- 
usually heavy  infestation  of  a  China  or  umbrella  tree  and  is  rarely 
exceeded,  wdiereas  an  average  of  50  or  60  per  square  inch  is  not  un- 
usual for  citrus  leaves.  In  the  case  of  China  and  umbrella  trees,  mi- 
grations are  evidently  due  to  lack  of  attractiveness  of  the  foliage  to  the 
adult  white  flies  at  the  times  when  the  migrations  occur.  There  are 
comparatively  few  live  larvae  and  pupae  on  the  foliage  after  the  middle 
of  August  at  Orlando.  The  greater  part  of  these  represent  delayed 
emergence  from  the  second  generation  of  white  Hies  and  not  the  result 
of  eggs  deposited  by  the  third  brood  of  adults.  This  supports  direct 
observations  to  the  effect  that  the  third  brood  of  adults,  which  is  con- 
cerned in  the  most  extensive  migrations,  deposits  practically  no  eggs 
on  the  China  and  umbrella  trees. 

China  and  umbrella  trees  as  a  factor  in  dissemination. — Umbrella 
and  China  trees  are  extensively  grown  throughout  the  Gulf  coast 
citrus-growing  regions,  and  they  are  almost  entirely  responsible  for 
the  hundreds  of  millions  of  adults  which  in  midsummer  appear  on 
the  wing  throughout  most  of  the  towns  where  the  citrus  white  fly 


46  WHITE   FLIES   INJURIOUS    TO   CITRUS    IN    FLORIDA. 

occurs.  That  these  are  principally  those  which  have  bred  upon 
China  and  umbrella  trees  is  shown  clearly  by  the  fact  that  at  Gaines- 
ville, Lake  City,  Tallahassee,  and  other  points  in  the  northern  part  of 
Florida,  where  other  food  plants  are  too  few  to  produce  noticeable 
numbers  of  migrating  adults,  the  numbers  are  apparently  not  less 
than  where  both  citrus  trees  and  China  and  umbrella  trees  are  exten- 
sively grown,  as  at  Orlando.  On  this  point,  Dr.  Berber  states:1 
"The  principal  food  plants  in  Gainesville  and  north  Florida  are  China 
and  umbrella  trees,  there  being  only  enough  citrus,  privet,  and  other 
evergreen  food  plants  to  bring  about  the  restocking  of  the  deciduous 
trees  every  spring."  These  considerations  indicate  very  positively 
the  main  source  of  the  enormous  number  of  migrating  adidt  flies  on 
trees  in  midsummer,  sometimes  observed  between  the  middle  of 
May  and  the  middle  of  June.  These  adults  are  the  second  brood  of 
the  season  and  the  first  to  mature  on  the  food  plants  mentioned.  The 
newer  growth  of  these  trees  is,  as  has  been  shown,  very  attractive  to 
the  adult  flies,  and  if  there  is  an  abundance  of  it  comparatively  few 
migrate.  The  third  brood,  composed  mainly  of  individuals  of  the 
second  and  third  generations,  matures  over  a  more  extended  period, 
in  general  covering  the  months  of  July  and  August  in  different  sec- 
tions of  Florida. 

Estimates  of  the  number  of  adult  citrus  white  flies  breeding  on 
umbrella  trees  and  on  citrus  trees  as  given  under  the  subject  of  food 
plants  have  shown  that  a  single  umbrella  tree  of  medium  size  may 
produce  as  many  adult  white  flies  by  midsummer  as  could  be  pro- 
duced on  7  acres  of  orange  trees.  The  maturity  of  so  many  adults 
on  single  trees,  and  their  migration  therefrom  hi  search  of  a  more 
desirable  food  supply  than  China  and  umbrella  trees  afford  in  mid- 
summer, cause  the  rapid  spread  of  the  pest  throughout  the  towns, 
directly  by  flight  of  the  adults  and  by  mediums  hereinafter  dis- 
cussed into  the  surrounding  country  and  from  town  to  town  along 
railway  lines  and  watercourses. 

Dissemination  by  flight  when  citrus  frees  only  are  concerned. — It  has 
been  shown  under  the  subject  of  food  plants  that  the  citrus  white  fly 
does  not  ordinarily  increase  to  the  point  of  overcrowding  on  grape- 
fruit. Migrations  of  adults  in  noticeable  numbers  from  solid  blocks 
of  these  trees  probably  never  occur  under  ordinary  circumstances, 
and  spread  through  such  blocks  or  groves  from  the  first  point  of  infes- 
tation is  very  slow  if  no  other  food  plants  are  concerned.  The  spread 
in  groves  of  orange  or  tangerine  trees  or  of  both  is  more  rapid,  but 
not  as  much  so  as  ordinarily  considered.  The  white  fly  is  rarely 
observed  during  its  first  year's  appearance  in  a  citrus  grove.  Atten- 
tion is  usually  first  attracted  to  its  presence  through  the  blackening 
of  foliage  on  one  or  a  few  trees.     This  blackening  of  foliage  in  itself 

1  Press  Bulletin  108,  Florida  Agriculture  Experimental  Station,  February  13,  1909. 


rill     CITBUfi   winii     i  i  \  :      i ■  i: i  \n.  1  7 

is  almost  positive  evidence  of  the  presence  of  the  fly  in  the  grove 
during  al  least  the  preceding  two  years  unless  the  infestation  is  due 
to  migrations  from  China  or  umbrella  trees  or  from  oversto< 
neighboring  citrus  groves.  In  such  cases  infestation  may  become 
quite  general  throughout  several  acres  in  one  season  and  extensive 
blackening  of  the  foliage  may  result  early  in  the  next  season,  or  in 
about  one  year  after  the  first  introduction.  In  the  case  of  uew  infes- 
tation in  any  locality,  however,  the  beginning  doubtless  is  usually 
the  introduction  of  a  few  insects  bj  some  one  of  the  means  herein- 
after discussed.  In  a  mixed  grove  of  tangerine  and  orange  the  pest 
is  discovered  first  as  a  rule  on  tangerine,  and  in  a  grove  of  seedling 
trees  with  a  few  budded  trees  intermixed  usually  the  latter  are  fust 
discovered  to  he  infested.  Many  citrus  growers  who  have  groves, 
such  as  those  mentioned,  and  who  have  watched  carefully  for  the 
appearance  of  the  pest  in  their  groves,  have  finally  found  it  well 
established  on  a  single  tangerine  or  budded  orange  tree  before  any 
evidence  of  the  presence  of  the  insect  was  observed  elsewhere. 
Through  tin1  hindrances  to  successful  establishment  and  the  checks 
on  multiplication,  principally  those  discussed  in  connection  with 
parthenogenesis  and  natural  mortality,  the  white  fly  frequently 
develops  so  slowly  after  its  first  introduction  that  it  may  not  increase 
to  the  point  where  it  is  usually  first  observed  for  three  or  four  yen-. 
It  is  a  common  error  to  consider  that  the  first  discovery  of  the  white 
fly  in  a  grove  is  an  indication  of  its  very  recent  introduction.  This 
may  or  may  not  be  the  case.  Usually  it  is  not  the  case.  It  should 
be  borne  in  mind  in  this  connection  that  in  the  most  careful  inspec- 
tion, even  by  a  competent  entomologist,  the  failure  to  discover  a 
single  specimen  of  the  white  fly  is  not  positive  proof  that  it  is  not 
present.  The  foregoing  generalizations  are  based  upon  many 
observations  by  the  agents  of  this  bureau  who  have  been  engaged  in 
these  investigations,  more  particularly  the  authors  of  this  bulletin 
and  Mi-.  W.  XV.  Yothers. 

The  rapidity  of  spread  into  a  citrus  grove  from  neighboring  infested 
groves  is  a  subject  which  becomes  temporarily  important  when  a 
nonisolated  grove  becomes  infested  for  the  first  time.  It  is  a  subject 
of  more  far-reaching  importance  in  connection  with  fumigation,  and  it 
is  in  this  connection  that  the  most  extensive  studies  in  this  line  have 
been  made.  The  result  of  these  studies  will  be  published  in  a  final 
report  on  fumigation. 

The  slowness  with  which  the  citrus  white  fly  increases  in  numbers 
and  spreads  from  the  first  point  of  infestation  has  been  noted  by 
many  citrus  growers  who  have  been  observant  enough  to  discover 
the  white  fly  soon  after  its  introduction  into  their  groves.  When 
the  rate  of  spread  of  the  white  fly  through  the  grove1  is  affected  by 
the  presence   of  migrating  adults  from  China  or  umbrella  trees,  the 


48  WHITE   FLIES   INJURIOUS   TO   CITEUS   IN    FLORIDA. 

difficulties  in  effectively  utilizing  artificial  checks,  spraying  and  fumi- 
gation, are  greatly  increased.  As  t  be  infested  area  in  a  newly  infested 
grove  or  locality  becomes  larger  the  rate  of  spread  by  flight  increases, 
aided  by  secondary  centers  of  infestation  which  become  established 
by  various  means. 

Winds. 

Light  winds  are  an  important  adjunct  to  flight  in  the  local  distri- 
bution of  adult  white  flies,  but  strong  winds  are  ordinarily  of  slight 
consequence.  The  effect  of  light  winds  is  shown  by  the  influence 
of  almost  imperceptible  movements  of  the  air  on  the  direction  of 
migrations.  This  is  especially  noticeable  in  the  vicinity  of  China 
and  umbrella  trees  during  a  season  when  adults  are  emerging  in  abun- 
dance. The  principal  effect  of  the  movement  of  the  air  under  such 
conditions  is  not  in  carrying  the  insects,  but  in  causing  the  flight 
energy  of  the  insect  to  be  expended  in  one  general  direction  rather 
than  to  be  wasted  in  zigzag  lines  with  comparatively  little  real  pro- 
gression. Other  conditions  being  equal,  the  adult  white  flies  migrate 
in  greatest  abundance  when  the  atmosphere  is  calmest,  and  con- 
versely show  the  least  tendency  to  migrate  in  strong  winds.  It 
is  possible  that  isolated  infestations  may  sometimes  result  from 
spread  of  adults  by  strong  winds,  but  it  is  seldom  that  there  is  not 
a  more  plausible  explanation  obtainable.  With  the  white  fly  pres- 
ent in  abundance  for  many  years  in  Orlando,  Fla.,  and  other  towns 
and  cities  in  important  orange-growing  sections  of  Florida,  the  fact 
that  there  are  still  many  noninfested  citrus  groves  within  a  radius 
of  5  miles  of  nearly  all  such  centers  of  infestation  is  in  itself  an  indi- 
cation of  the  minor  influence  of  winds  in  this  connection.  Strong 
breezes  or  winds  exert  some  check  on  the  spread  of  adults  by  causing 
them  to  cling  tenaciously  to  their  support,  as  pointed  out  by  Prof. 
H.  A.  Gossard.1 

VEHICLES,  RAILROAD    TRAINS,  AND    BOATS. 

In  towns  in  Florida  where  the  citrus  white  fly  occurs  and  China 
trees  and  umbrella  trees  are  abundant  it  is  a  matter  of  common 
observation  that  during  the  periods  of  migration  large  numbers  of 
adults  alight  upon  automobiles,  carriages,  wagons,  and  railroad  coaches. 
The  authors  have  seen  covered  carriages  with  more  than  100  adults 
resting  on  the  inside  of  the  top  and  sides.  In  driving  through  a 
heavily  infested  citrus  grove  in  late  afternoon  at  certain  seasons, 
hundreds  of  adults  may  be  observed  on  the  carriage  (PL  VI,  fig.  2). 
Newly  infested  groves  show  the  first  infestation  so  frequently  on  trees 
close  to  a  driveway  or  road  that  conveyance  of  the  citrus  white  fly  by 
means  of  carriages,  wagons,  and  automobiles  must  be  considered  one  of 
the  most  important  methods  of  spread  from  town  to  surrounding 

1  Bulletin  67,  Florida  Agricultural  Experiment  Station,  p.  13. 


' 


p 


Dissemination  of  White  Flies. 

Fig.  1.— Nursery  citrus  trees  infested  with  white  flies  set  out  in  an  isolated  noninfested  grove 
without  having  leaves  removed.  Fig.  2.— Buggy  in  an  orange  grove:  buggy  top  full  of  adult 
white  flies  ready  to  be  carried  to  other  groves.  Fig.  3.— Train  at  station:  adult  citrus  white 
flies  swarming  from  near-by  umbrella  China  trees  into  coaches  ready  to  be  carried  for  miles 
down  the  Florida  east  coast.     (Original.) 


PHB  CITRUS  WHIT!     FLY :   SPREAD.  1!) 

country  or  from  grove  i<>  grove.     Ai  Orlando,  In  July,  1906,  adult 

citrus  white  flies  were  observed  late  in  the  aften n  alighting  on  the 

sides  of  coaches  and  flying  into  the  windows  and  doors  of  coaches 
of  a  passenger  train  standing  at  a  railroad  station  (PL  \  I,  li. 
Hundreds  of  adults  were  carried  we&i  toward  Wildwood  through 
points  which,  so  far  as  known,  were  not  infested  at  the  time.  The 
presence  of  China,  umbrella,  or  citrus  trees  near  railroad  stations 
increases  the  chances  for  successful  introduction  l>\  railroad  trains. 
[n  this  connection  the  recent  action  of  the  Atlantic  Coast  Line  Rail- 
road and  Seaboard  Air  Line  Railway  in  destroying  such  trees  along 
their  right  of  way  is  to  be  commended.  A  map  of  Florida  showing 
the  distribution  of  the  citrus  white  fly  plainly  indicates  the  relation 
between  the  railroads  and  the  main  lines  of  dissemination.  This  is 
shown  in  an  incomplete  way  by  figure  2,  in  which  are  given  the  points 
infested  by  the  citrus  white  fly  in  Florida  according  to  the  records 
made  in  connection  with  the  present  investigation  and  such  other 
records  as  are  undoubtedly  correct  or  which  have  been  verified.  The 
infestation  at  Arcadia,  Fla.,  first  discovered  in  January,  1907,  but 
which  probably  resulted  from  an  introduction  of  citrus  white  flies 
in  1905,  was  with  little  doubt  due  to  the  introduction  of  adult  Hies 
by  means  of  railroad  trains.  An  examination  of  the  situation  in 
February,  1907,  by  the  senior  author  showed  the  center  of  infestation 
to  be  located  near  railroad  stations,  and  careful  inquiry  concerning 
other  possible  sources  showed  that  railroad  trains  were  the  most 
likely  means  of  introduction.  North  of  Arcadia  no  nearer  infested 
point  was  known  than  Bartow  and  toward  the  south  no  nearer 
infested  point  than  Fort  Myers.  The  distance  in  each  case  was  about 
40  miles.  So  far  as  known  there  were  at  that  time  no  intermediate 
points  infested  between  Arcadia  and  the  two  points  mentioned. 
Here  again  the  factors  unfavorable  to  the  successful  establishment 
of  the  pest  in  a  previously  uninfested  locality  play  an  important  role, 
as  shown  by  the  fact  that  even  at  the  present  writing  the  citrus  white 
fly  is  not  generally  distributed  between  Bartow  and  Fort  Myers. 
As  we  have  no  record  and  have  heard  no  report  of  the  occurrence  of 
the  fly  at  any  other  point  than  Arcadia,  it  is  unlikely  that  other 
infested  points  exist. 

Steamboats  are  used  quite  extensively  on  the  rivers  and  along  the 
coast  of  Florida  in  transporting  citrus  fruits  and  have  in  a  degree  a 
similar  status  to  railroad  trains  in  transporting  the  citrus  white  fly. 

Citrus  Nursery  Stock  and  Ornamental  Plants. 

The  carriage  of  the  citrus  white  fly  in  its  egg,  larval,  and  pupal 
stages  by  means  of  citrus  nursery  stock  (PL  VI,  fig.  1)  and  ornamental 
plants  has  always  been  an  important  factor  in  the  spread  of  the 

86850°— Bull.  92—11 1 


50  WHITE   FLIES   INJURIOUS   TO   CITRUS    IN    FLORIDA. 

insect.  The  citrus  white  fly  was  without  doubt  introduced  into  the 
United  States  and  distributed  to  the  most  important  centers  of 
infestation  by  this  means.  In  Florida  the  white  fly  was  probably 
introduced  first  on  citrus  nursery  stock  into  some  citrus  grove  on  the 
St.  Johns  River  in  St.  Johns  County,  and  later  by  the  same  means 
into  Manatee  and  Fort  Myers.  Gainesville,  Ocala,  Orlando,  and 
Bartow  were  probably  among  the  points  to  which  the  white  fly  was 
introduced  on  nursery  stock.  The  distribution  of  the  citrus  white 
fly  along  the  Gulf  coast  citrus-growing  regions  west  of  Florida  has 
been  largely  due  to  shipments  of  infested  citrus  nursery  stock, 
umbrella  trees,  privets,  and  cape  jessamines.  Of  all  methods  of 
spread  which  are  operative  over  greater  distances  than  the  flight  of 
adults,  introductions  of  live  immature  stages  on  trees  or  shrubs  for 
transplanting  purposes  are  by  far  the  most  certain  to  result  in  the 
successful  establishment  of  the  species.  Fortunately  it  is  practicable 
to  prevent  spread  by  this  method  by  defoliating  the  trees  as  they  leave 
the  nursery.  Much  has  been  accomplished  in  the  past  by  individual 
citrus  growers,  but  more  attention  should  be  given  to  this  matter  in 
communities  not  now  infested  by  both  of  the  white  flies  treated  in  this 
bulletin. 

Accidental  Spread  by  Man. 

Carriage  oj  the  adult  white  flies  on  human  beings. — Man  is  doubtless 
responsible  to  a  limited  extent  for  the  spread  of  adult  white  flies. 
During  migrating  periods,  when  in  heavily  infested  orange  groves  or 
in  towns  where  there  are  infested  China  and  umbrella  trees,  adults  are 
frequently  observed  on  the  clothing.  Prof.  H.  A.  Gossard  states 
that  he  has  carried  adult  white  flies  for  nearly  half  a  mile  on  his 
clothing  after  standing  beneath  a  heavily  infested  tree. 

Introduction  in  pickers'  outfits. — In  some  instances  the  citrus 
white  fly  is  believed  to  have  been  introduced  into  previously  unin- 
fested  localities  by  orange  pickers.  In  this  case  the  principal  danger 
lies  in  introducing  live  pupae  on  citrus  leaves  accidentally  brought 
in  with  picking  sacks  and  field  boxes.  The  authors  consider  that  there 
is  practically  no  danger  of  the  carriage  of  adults  of  the  citrus  white 
fly  by  pickers'  outfits  between  December  1  and  March  1.  The  few 
adults  present  in  citrus  groves  during  this  period  would  rarely  result 
in  their  transference  to  uninfested  groves  by  such  means,  and  the 
unfavorable  factors  heretofore  discussed  would  almost  certainly 
prevent  the  successful  establishment  of  the  pest.  It  would  be 
almost  impossible  to  conceive  of  any  likely  method  by  which  a  suc- 
cessful introduction  of  the  citrus  white  fly  into  a  noninfested  grove 
could  be  accomplished  by  the  carrying  of  leaves  infested  by  eggs  or 
larvae.  Leaves  infested  with  live  pupae,  however,  particularly  about 
the  time  of  the  beginning  of  emergence  of  the  first  spring  brood, 


I  ii  i    CUTBUS  WHIT!     i  i.v  :    LIP]     HIE  rORI     \M»   HAB1  C8.  5  1 

might  readily  produce  a  sufficient  aumber  of  adulte  to  successfully 
establish  the  pest.  Such  leaves,  after  introduction,  would  u<'<-d  to 
have  ;i  favored  location,  for  exposure  i<>  much  sunlight  or  to  too 

much  moisture  would  soon  destroy  the  insects. 

Introduction  on  leaves  infested  with  parasitic  fungi.  The  matter  of 
spread  of  the  white  fly  in  connection  with  the  attempt  to  introduce 
parasitic  Fungi  i>  a  subject  of  considerable  importance.     The  danger 

here  is  due  to  the  failure  to  recognize  the  distinction  between  the 
citrus  white  fly  (Aleyrodes  citri)  ami  the  cloudy-winged  white  fly 
(Aleyrode8  nubifera).  The  owner  of  8  grove  infested  by  the  latter 
species  only,  would  provide  a  very  favorable  opportunity  for  the 
introduction  of  the  first  and  most  destructive  species  if  in  introduc- 
ing parasitic  fungi  he  should  obtain  his  supply  of  leaves  from  certain 
sections  of  Florida,.  The  spread  of  the  cloudy-winged  white  fly  has 
been  encouraged  in  a  similar  manner.  The  tree-planting  method  of 
introducing  the  fungi,  especially  the  brown  fungus,  is  the  most  dan- 
gerous practice  in  this  connection.  Of  somewhat  less  danger  in  the 
individual  cases,  but  of  far  greater  danger  on  account  of  the  more 
frequent  opportunities  presented,  is  the  introduction  of  fungus- 
infected  leaves  for  pinning  or  for  spraying  the  spores.  The  pinning 
of  leaves  as  a  means  of  introducing  the  parasitic  fungi  has  little  more 
to  recommend  it  than  the  tree-planting  method,  but  it  has  without 
doubt  been  the  means  of  introducing  the  citrus  white  fly  on  many 
occasions.  Leaves  introduced  for  the  spore-spraying  method  of 
spreading  the  fungus  parasites  are  an  element  of  much  danger  under 
certain  conditions.  Some  sections  of  Florida  in  which  only  the  cloudy- 
winged  white  fly  occurs  are  in  more  danger  of  having  the  citrus  white 
fly  introduced  by  some  uninformed  person  in  this  way  than  they  are 
of  its  introduction  in  any  other  manner.  Specific  examples  might  be 
cited  where  the  introduction  of  either  A.  citri  or  A.  nubifera  was 
with  little  doubt  due  to  introducing  fungus-infected  leaves  or  trees, 
but  the  danger  is  too  obvious  to  require  further  discussion  in  this  place. 

LIFE    HISTORY    AND    HABITS. 

Summary. 

The  eggs  of  the  citrus  white  fly  (fig.  3)  are  laid  scatteringly,  with 
fewr  exceptions,  on  the  underside  of  the  leaves  of  the  various  food 
plants,  and  hatch  in  from  8  to  24  days,  according  to  the  season. 
During  ordinary  summer  weather  from  75  to  100  per  cent  hatch 
on  the  tenth  to  twelfth  day.  Infertile  eggs  hatch  as  readily  as  fertile 
eggs  and  produce  adults  of  the  male  sex  only.  After  hatching,  the 
young  larva  (figs.  4-6)  actively  crawls  about  for  several  hours,  when 
it  ceases  to  crawl,  settles  upon  the  underside  of  the  leaf,  and  begins 
to  feed  by  sucking  the  plant  juices.     It  molts  three  times  before 


52  WHITE   FLIES   INJURIOUS   TO   CITRUS   IN   FLORIDA. 

becoming  a  pupa.  After  the  first  molt  (see  fig.  7)  the  legs  become 
vestigial;  hence  (hereafter  it  is  impossible  for  it  to  materially  change 
its  location  upon  the  leaf.  Larval  life  averages  in  length  from  23  to 
80  days.  The  pupa  (fig.  9)  closely  resembles  the  grown  larva  (fig.  8) 
and  requires  from  13  to  304  days  for  development.  The  adult  fly 
(Hg.  10)  has  an  average  life  of  about  10  days,  although  several  females 
have  been  Known  to  live  27  days.  Females  may  begin  depositing 
eggs  as  soon  as  6  hours  after  emergence  and  continue  ovipositing 
throughout  life.  The  maximum  egg-laying  capacity  is  about  250 
eggs,  although  150  more  nearly  represents  the  number  laid  under 
grove  conditions.  Unfertilized  females  deposit  as  many  eggs  as 
fertile  females. 

The  entire  life  cycle  from  egg  to  adult  requires  from  41  to  333 
days;  the  variation  in  the  number  of  days  required  from  eggs  laid 
on  the  same  leaf  on  the  same  day  is  very  remarkable.  During  the 
course  of  the  year  the  fly  may  pass  through  a  minimum  of  two  gen- 
erations and  a  maximum  of  six  generations.  The  generation  started 
by  the  few  adults  that  emerge  during  the  winter  is  entirety  dependent 
upon  weather  conditions  and  may  or  .may  not  occur.  Each  genera- 
tion except  those  started  after  the  middle  of  August  is  more  or  less 
distinctly  two-brooded. 

Methods  of  Study. 

As  it  is  impossible  to  rear  citrus  white  flies  through  their  entire 
life  cycle  on  detached  leaves,  a  gauze-wire  cage  was  devised  by  the 
senior  author  which  has  proved  of  great  value  and  convenience  in 
carrying  on  life-history  studies  under  conditions  as  nearly  normal  as 
it  is  possible  to  get  them.  This  cage  (PL  VII),  which  is  cylindrical 
in  shape  and  open  at  one  end,  may  be  made  any  size,  but  one  6 J 
inches  long  by  3J  inches  in  diameter  has  proved  most  convenient. 
It  can  easily  be  made  by  fashioning  two  rings  of  heavy  wire  to  which 
is  soldered  the  wire  gauze,  as  shown  in  the  illustration.  To  the  open 
end  is  attached  a  piece  of  closely  woven  cheesecloth  long  enough 
to  extend  about  4  inches  beyond  the  cage.  After  the  leaf,  or  leaves, 
to  be  caged  have  been  cleaned  of  all  stages  of  the  white  fly  by  means 
of  a  hand  lens  and  cloth,  the  cage  is  slipped  over  the  foliage.  The 
adult  flies  are  then  introduced,  if  desired,  and  the  cloth  attached  to 
the  cage  wrapped  around  the  stem  of  the  shoot  or  petiole  of  the  leaf, 
as  the  case  may  be,  in  such  a  manner  that  the  flies  can  not  escape 
nor  the  ants  and  other  predaceous  insects  enter.  To  keep  the  entire 
weight  of  the  cage  from  falling  on  the  petiole  of  the  leaf  or  its  short 
stem,  and  to  regulate  the  position  of  the  leaf  within  the  cage,  a  cord 
is  tied  around  the  outer  end  of  the  cage  and  attached  by  the  loose 
end  to  a  convenient  branch. 


Plati    VII. 


Cages  for  Rearing  White  Flies. 
Fig.  1.— Rearing  cages  in  position  on  orange  trees.     Fig.  'J.— Enlarged  rearing  cage.    (Original.) 


i  it  i    .11  ins  u  ii  ri  i    fly:  i  iii.  in-  rom    vnd  iiabii 


\  \,.|\  satisfactory  method  of  deflniterj  marking  larvae  in  order 
that  no  mistake  ma)  be  made  in  Identifying  field  notes  with  the 
individual  larvae  i<»  which  bhev  refer,  is  to  scratch  lightly  on  the 
epidermis  of  the  leaf,  with  a  thorn  or  pin,  a  bracket  or  other  mark 
and  outside  this  a  Dumber  thai  shall  correspond  with  that  used  in 
the  note  book,  [n  marking  larvae  care  should  be  in  ken  in  scratching 
the  leaf  to  allow  for  the  future  Lrn<\\  th  of  the  insect  and  not  to  injure 
the  epidermis  of  the  leaf  too  severely  ,  [n  this  manner  a  large  number 
of  Ian  83  \\  ere  marked  as  soon  as  the)  settled  and  their  gro^  th  noted 
l»\  daily  obsen  at  ions. 

In  determining  the  sums  of  effective  temperature,  t3    F.  has  been 
taken   as  a    basis    in   accordance  with    Dr.   Merriam's  general    law 
although  this  has  led  to  certain  inaccuracies  of  which  the  authors 
are  aware.     The  determination  of  the  effective 
temperature  in  the  case  of  the  white  fly  would 
requires  special  study  which  it  has  been  imprac- 
ticable to  undertake. 

Th  i.  Egg. 

description. 

The  eggs  of  the  citrus  white   flv  (fig.  3)  are  so 

•  '  ■  Fig.  3.— The  citrus   white 

small   that    they   appear  to  the  unaided  eye  as       ny(Aieyrodt 
fine  particles  of  whitish  dust  on  the  under  sur-       Greatly  enlarged. 
face  of  the  leaves.     Their  minute  size  is  empha- 
sized by  the   fact    that  118  placed  end  to  v\u\  would   measure4  hut    an 
inch,  while  about  35,164  could  be  placed  side  by  side  in  one  square 
inch.     Under  the  magnifying  lens  they  appear  as  smooth,  polished, 
greenish-yellow  objects  shaped   much  like  a  kernel  of  wheat.     Fol- 
lowing is  a  more  minute  description: 

Length,  0.2-0.23  una.;  width,  0.08-0.09  mm.  Surface  highly  polished,  without 
sculpturing,  color  pale  yellow  with  faint  greenish  tinge  when  first  deposited,  paler  than 
the  under  surface  of  the  leaf.     Egg  elongate,  Bubellipsoid,  slightly  wider  beyond  the 

middle  or  at  about  the  point  where  the  eyes  of  the  embryo  subsequently  appear;  borne 
at  end  of  a  comparatively  slender  brownish  petiole  or  footstalk,  slightly  shorter  than 
the  width  of  the  egg,  and  somewhat  knobbed  at  bas 

As  the  embroyo  approaches  maturity  its  purple  eyes  may  be  seen 
showing  distinctly  through  the  egg  membranes  at  a  point  beyond  the 
middle  of  the  egg.  At  about  this  time,  also,  the  hitherto  uniformly 
colored  egg  contents  become  orange  or  golden  at  the  proximal  end  and 
whitish  translucent  on  the  distal  three-fourths.  The  egg  surface 
sometimes  assumes  a  white  pruinose  appearance,  due  to  the  presence 
of  wax  rubbed  from  the  bodies  of  the  adults  while  crawling  over  the 
deposited  on  leaves  from  which  the  adults  have  been 
excluded  after  v^  deposition  do  not  show  this  pruinose  condition. 


54  WHITE   FLIES   INJURIOUS   TO   CITRUS   IN   FLORIDA. 

Eggs  in  which  the  embryonic  development  is  normal  do  not  turn  dark 
in  color,  but  those  killed  through  attack  by  thrips  or  by  other  agency 
frequently  become  bronze  colored,  thus  resembling  the  eggs  of  A. 
nubifera  from  which  the  waxy  sculpturings  have  been  rubbed. 

DURATION    OF    EGG     STAGE. 

That  no  doubt  might  arise  concerning  the  exact  age  of  the  eggs 
used  in  obtaining  the  data  incorporated  into  Table  VIII,  suitable 
leaves  were  selected  from  which  all  eggs  previously  deposited  were 
carefully  removed  by  the  aid  of  the  hand  lens  and  a  cloth.  Similar 
attention  wras  given  the  leaf  petiole  and  the  stalk,  and  wads  of  cotton 
wrere  tied  about  the  latter  both  above  and  below  the  leaf  to  prevent 
crawling  }Toung  from  reaching  the  leaf  along  the  petiole  (PI.  VII,  fig. 
1).  These  preliminary  steps  completed,  a  rearing  cage  containing 
adult  wThite  flies  was  placed  over  the  leaf  and  allowed  to  remain  the 
length  of  time  desired,  usually  from  1  to  24  hours,  with  preference 
shown  the  latter  number.  The  cage  was  then  removed  and  an 
empty  one  put  in  its  place.  By  this  method  all  doubt  was  removed 
as  to  the  period  of  time  over  which  deposition  took  place.  As  there 
is  scarcely  a  leaf  in  a  grove  infested  with  the  citrus  white  fly  that 
does  not  bear  from  a  few  to  many  eggs,  this  becomes  an  important 
point  and  failure  in  its  recognition  has  led  in  the  past  to  statements 
greatly  underestimating  the  minimum  duration  of  the  egg  stage  dur- 
ing the  warmer  months. 


I  II  I     CITRUS    WHITE    UN 


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56  WHITE   FLIES   INJURIOUS   TO   CITRUS   IN   FLORIDA." 

The  conclusions  presented  herewith  are  drawn  from  the  data  pre- 
sented in  Table  VIII,  based  upon  daily  observations  of  over  5,000 
eggs  deposited  at  intervals  from  February  to  October.  From  these 
and  other  data  not  included,  it  can  be  stated  that  the  eggs  hatch  dur- 
ing a  period  of  from  8  to  24  days  after  deposition,  according  to  the 
season  of  the  year.  While  there  are  no  data  regarding  the  length  of 
the  incubation  period  for  eg^  deposited  by  the  few  female  flies  occa- 
sionally seen  during  the  winter  months,  as  noted  under  seasonal  his- 
tory, it  is  probable  that  hatching  extends  over  even  a  greater  number 
of  days  during  the  winter  season.  The  deposition  of  such  eggs  is, 
however,  a  comparatively  rare  occurrence  and  will  receive  no  further 
mention  here.  Jn  no  instance  have  eggs  been  seen  to  hatch  before 
the  eighth  day  from  deposition,  even  during  the  months  July  and 
August,  1907,  when  the  average  mean  temperatures  were  slightly 
above  normal,  while  under  the  most  favorable  summer  weather  con- 
ditions from  75  to  100  per  cent  of  the  eggs  hatch  during  the  period 
from  the  tenth  day  to  the  twelfth  day  from  deposition. 

In  general,  the  warmer  the  season  the  shorter  and  more  nearly  uni- 
form is  the  period  of  egg  development  or  incubation.  During  the 
months  of  July  and  August,  when  the  normal  monthly  temperatures 
at  Orlando  range  from  about  72°  F.  as  the  mean  of  the  minimums  to 
about  93°  F.  as  the  mean  of  the  maximum  records,  practically  all  the 
eggs  hatch  from  the  tenth  day  to  the  twelfth  day.  Even  at  this  most 
favorable  season,  in  one  instance  hatching  was  delayed  for  19  days. 
During  the  somewhat  cooler  weather  of  late  September  and  early 
October  and  the  decidedly  cooler  months  of  February,  March,  and 
April,  hatching  is  more  or  less  delayed  according  to  the  prevailing 
temperature  and  is  scattered  over  a  larger  number  of  days.  This 
same  result  is  brought  about,  only  in  a  less  degree,  by  a  cool  period 
occurring  in  an  otherwise  warm  season,  as  shown  under  record  4 
(Table  VIII). 

Reference  to  the  daily  rate  of  hatching  in  Table  VIII,  and  to  the 
accompanying  degrees  of  accumulated  effective  temperatures,  shows 
that  regardless  of  the  time  of  year  deposited  and  the  number  of  da}rs 
required  for  incubation,  over  90  per  cent  of  the  eggs,  on  an  average, 
hatch  between  the  accumulation  of  from  375°  to  475°  of  effective 
temperature. 

Exception  to  this  statement  must  be  taken  in  records  1  and  2 
(Table  VIII).  The  number  of  degrees  of  effective  temperature 
required  seems  to  be  greater  at  this  season,  although  this  might  not 
prove  to  be  the  case  if,  as  is  probable,  an  error  has  arisen  from  using 
43°  F.  as  the  basis  for  calculating  the  effective  temperature. 

Reference  to  the  two  preceding  tables  shows  that  considerable 
variation  exists  in  the  length  of  the  egg  stage  among  eggs  deposited 
on  the  same  day,  or  even  within  the  same  hour,  and  subsequently 


I  ii  I    CITRUS   will  ii     PLY:    i.i  l  i     HI8T0B1     1ST)   HAB1  57 

subjected  to  identical  conditions  of  heal  and  moisture.  Even  when 
hatching  was  most  concentrated  during  the  heat  <>f  Bummer  and  99  s 
per  cenl  of  1 1  »<*  eggs  hatched  on  the  tenth  and  eleventh  days  from 
dale  of  deposition,  hatching  extended  over  a  period  of  from  9  to  19 
days.  [latching  over  a  period  of  from  6  to  7  days  alter  the  firsl 
crawling  young  appears  is  an  ordinary  occurrence  during  the  cooler 
portions  of  the  season  of  activity.  In  this  respect,  white-fly  eggs  are 
markedly  different  from  the  eggs  of  most  other  insects  deposited  in 
batches  which  usually  hatch  within  one  or,  at  the  most,  a  lew  hours 
of  each  other. 

PARTS  ENOGEN  B8IS. 

The  existence  of  parthenogenesis  among  aieyrodids  was  first  rec- 
ognized by  the  senior  author ]  in  connection  with  his  investigations 
of  the  greenhouse  white  fly  (.1.  vaporariorum) .  His  prediction  at  thai 
time  that  this  method  of  reproduction  would  ultimately  be  proved  to 
occur  among  many  if  not  all  t  lie  species  of  Aleyrodes  ha-  been  strength- 
ened by  t  he  results  of  the  present  investigations.  While  there  are  no 
definite  data  to  the  effect  that  parthenogenetic  eggs  are  deposited 
under  natural  conditions,  there  is  practically  no  doubt  that  such  depo- 
sition does  occur,  especially  by  females  not  yet  mated  or  by  females 
appearing  at  unseasonable  times  or  when  males  are  decidedly  in  the 
minority.  Scattered  females  emerging  during  the  winter,  or  resulting 
from  the  comparatively  few  pupae  surviving  fumigation,  either  never 
have  the  opportunity  to  mate  or  deposit  many  of  their  vggs  before 
such  opportunity  presents  itself. 

That  virgin  females  of  A.  citri,  emerging  from  pupse  kept  separately 
in  vials,  and  later  confined  in  rearing  cages  under  normal  grove  con- 
ditions, except  for  the  exclusion  of  males,  will  readily  deposit  the  nor- 
mal number  of  eggs,  and  that  these  eggs  will  develop  normally  and 
will  produce  adults  of  the  male  sex,  has  been  thoroughly  demonstrated. 
Of  the  Give  separate  cage  experiments  started  with  parthenogenetic 
eggs,  all  of  111  adults  emerging  in  four  of  the  cages  were  males,  while 
of  "Jos  more  adults  emerging  from  the  fifth  cage,  all  but  4  individuals 
were  males;  the  4  females  emerging  under  such  conditions  as  to  lead 
to  the  supposition  that  they  came  from  fertile  eggs  overlooked  in 
preparing  the  leaf  for  the  experiment. 

HATCHING. 

In  hatching,  the  egg  membranes  rupture  at  the  end  opposite  the 
pedicel,  and  then  split  down  vav\\  side1  sufficiently  to  permit  the 
young  Larva  to  crawl  out.  The  glistening  eggshell,  somewhat  resem- 
bling in  appearance  a  bivalve  shell,  eventually  becomes  shriveled 
and  loses  its  original  form. 

1  Notes  <>n  Some  Aleyroded  from  Massachusetts,  with  Descriptions  of  New  Species. 
Psyche,  April,  1903,  p.  81.     Technical  Bulletin  No.  1,  Mass.  Agr.  Exp.  Sta.,  pp.  31-33. 


58  WHITE    FLIES   INJURIOUS   TO    CITRUS    TX    FLORIDA. 

Proportion  of  eggs  that  hatch. — Observations  covering  many  thou- 
sands of  eggs,  both  in  the  cage  experiments  and  in  the  grove,  have 
demonstrated  that  the  number  of  eggs  that  fail  to  hatch  is  too  insig- 
nificant and  has  too  little  practical  bearing  to  warrant  the  collection 
of  data  on  this  point.  It  is  safe  to  say  that  considerably  less  than  1 
per  cent  do  not  hatch.  In  fact,  it  seems  evident  that  no  egg  would 
fail  to  hatch  except  owing  to  the  dropping  of  the  leaf  or  unless  sub- 
jected to  attack  from  without.  In  many  instances  failure  to  hatch 
can  be  directly  traced  to  attack  by  several  species  of  insects  and  a 
fungous  parasite. 

Effect  of  drying  of  leaves  on  hatching. — In  10  instances  leaves  bearing 
many  thousand  eggs  were  so  placed  that  the  eggs  were  exposed  to 
direct  sunlight  or  to  partial  shade,  and  although  frequent  observa- 
tions were  made  none  of  the  eggs  were  known  to  hatch.  In  general 
the  drying  of  leaves  to  which  eggs  are  attached  prevents  hatching  of 
all  except  those  eggs  containing  nearly  mature  embryos.  This  fea- 
ture is  probably  common  to  all  aleyrodids,  since  the  senior  author 
has  noted  a  similar  occurrence  in  the  case  of  the  greenhouse  white  fly 
(A.  va porariorum) . 

The  Larval  and  Pupal  Stages, 
description  of  stages. 

THE   LARVA. 

The  larvae  1  are  thin,  translucent,  elliptical,  scalelike  objects,  found 
usually  on  the  underside  of  the  leaves,  though  more  rarely  upon  the 
upper  surface.  When  normally  attached  to  the  leaf  they  are  so' 
nearly  transparent  as  to  be  seen  with  difficulty.  They  readily 
become  visible,  however,  by  either  bending  or  rubbing  the  fingers 
along  the  opposite  side  of  the  leaf,  thus  loosening  them  and  allowing 
the  air  to  get  beneath  them.  They  then  appear  whitish  (PI.  X,  fig.  2). 
So  very  inconspicuous  are  the  live  larvae  and  their  attack  so  unac- 
companied by  any  visible  effects  on  the  leaves,  aside  from  the  black- 
ening of  the  foliage,  that  their  presence  is  very  frequently  overlooked 
by  the  casual  observer.     A  detailed  description  follows: 

First  instar  larva  (figs.  4-6).  Length,  0.3  to  0.37  mm.;  width,  0.182  to  0.22  mm. 
Body  flat,  soalelike,  somewhat  swollen  ventrally,  especially  in  the  eephalothoracic 
region;  margin  entire,  with  30  small  tubercles,  each  bearing  a  horizontally  directed 
spine  of  which  6  cephalic  and  4  anal  are  proportionately  longer.  Spines  of  second 
pair,  counting  from  anterior  end  of  body,  arising  from  tubercles  not  on,  but  slightly 
posterior  to,  margin  on  ventral  surface.  Relative  lengths  of  the  15  pairs  of  spines  as 
follows: 

Pair    1      _2_3^A      5        6      7     10     11     12     13     14       15 
Spaces  ll'    9.8'    ll'    6.5'   5.4'    5.5'    6'    4'    4'    4 '    18'   5.4'   18.5' 

'The  larvae  and  pupae  are  frequently  called  by  many  growers  the  "egg"  of  the 
white  fiv.  This  misapplication  of  terms  should  be  discouraged  as  it  leads  to  unde- 
sirable confusion  when  referring  to  the  various  stages  through  which  the  white  fly 
passes  during  its  growth  from  egg  to  adult. 


I  II  I      (II  RTS    WHIM      I  IN 


I      HISTORY      \ N I >     I  I  \  I  ■ 


Fig.  4.—  The  citrus  white  fly: 
Crawling  young;  firsl  In- 
star,  dorsal  view.  <  .really 
enlarged.    (Original.) 


v,  marginal  wax  fringe  appear*  before  or  after  crawling  youi  Cephalo 

thoracic  and  thoracic  articulations  invisible  ibl)  9  abdomii 

Been  with  little  difficult}  Segments  al  posterior  end  of  body  modified  bj  vasiform 
orifice.  Latter  nearlj  Bemicircular  in  outline,  somewhal 
than  wide,  bordered  laterally  b)  chitinoue  thicken 
ings  which  do  doI  meet  posteriori)  ;  operculum  semicircu- 
lar, oearl}  equaling  in  Bize  the  vasiform  orifice  itself,  cover 
ing  the  ligula  and  bearing  on  its  median  posterior  margin 
what  appear  to  be  two  pair-  of  -mall  Bpines,  the  penulti- 
mate pair  of  which  is  aboul  twice  as  Inn- a-  the  ultimate. 
Ligula  darker  in  color  and  broadly 
.■nt  ic  in  Bhape.  <  >n  either  side 
of,  ami  slightly  anterior  to,  the  vasi- 
form orifice  is  a  short  backwardly 
directed  Bpine  arising  from  a  -mall 
tubercle.  The  two  pairs  of  rounded, 
simple,  reddish-brown  eyes,  less 
than  o.oi  mm.  in  diameter  and  0.096 
mm.  apart — a  dorsal  pair  and  a  ven- 
tral pair  are  situated  mesad  and 
slightly  anterior  to  the  fifth  pair  of 
marginal  spines,  the  dorsal  pair  be- 
ing  nearer  the  margin  and  slightly 
anterior  to  the  ventral  pair. 

Antennae,  legs,  and  mouth-parts  on  the  venter.  Antennae 
anterior  and  mesad  to  the  anterior  pair  of  legs,  0.1  mm.  long, 
very  Blender;  apparently  4-segmented,  articulations  between 
the  segments  seen  with  difficulty  and  frequently  that  be- 
tween the  third  and  fourth  entirely  wanting,  while  in  a  few 
specimens  the  second  segment  appears  to  be  divided  into 
two  parte:  Segmenl  1  short,  stout,  fleshy;  segment  2  one-half 
as  wide  and  twice  as  long  as  Begmenl  1 ;  Begment  3  narrower  than  segment  2  and  about 
four  times  as  long;  segment  4  very  slender,  less  than  one-half  as  long  as  segment  3,  and 
bearing  on  its  proximal  posterior  side  a  minute  spine,  and  distally  a  long  Bpine.  Legs 
short,  moderately  stout,  where  ex- 
tended about  one-third  the  width  __,— — ^- 


of  the  body;  coxae  very  short  and 
stout,  the  two  posterior  pairs  on 

the  posterior  inner  side  with  a 
moderately  stoul  Bpine  about 
equal  in  length  to  the  diameter  of 
the  coxae  and  directed  backward 
and  inward;  trochanters  distin- 
guished with  difficulty,  about 
one-third  as  long  as  wide  and 
collar-shaped;  femora  more  elon- 
gate, Blightly  tapering  distally, 
about  lour  times  as  long  as  tro- 
chanters; tibia?  much  narrower, 
somewhat  longer  than  the  femora, 
with  numerous  short  bristles,  two  on  the  outer  proximal  portion  longer  and  more  easily 
seen,  on  the  outer  distal  portion  with  a  long  bristle  forwardly  directed  and  curving 
inward  toward  the  tip  of  the  tarsi;  tarsi  short,  ending  distally  in  au  enlarged  disk- 
like process 


Fig.  5.— The  citrus  white 
fly:  Crawling  young;  first 
instar,  ventral  view, 
('.really enlarged.  (Orig- 
inal.) 


Fig.  0.— The  citrus  white  fly:  Antennae  and  left  hind  leg, 
first  instar.     Highly  magnified.     (Original.) 


60 


WIMTK    PLIES    INJURIOUS    TO   CITRUS   IN    FLORIDA. 


Fig.  7.— The  citrus  white 
fly:  Second  larval  instar, 
ventral  view.  <  J reatly  en- 
larged.   (Original.) 


Midway  between  the  anterior  pairs  of  legs  in  the  middle  of  the  body  is  the  fleshy 

mouth  papilla  from  which  arise  the  mouth  setae,  at  first  when  bent  backward  reaching 
only  to  slightly  beyond  the  posterior  coxae,  but  later  becoming  more  elongate.  Ante- 
rior to  the  mouth  papilla  is  the  semiovate  prostomal  plate,  extending  anteriorly  as 
far  as  a  line  connecting  the  antennae,  and  divided  longitudinally  by  two  curved 
sutures  into  one  elongate  median  and  two  shorter  lateral  pieces.  At  the  anterior  end 
of  the  prostomal  plate  is  a  pair  of  small  papilla?,  each  papilla 
bearing  a  small  forwardly  directed  spine. 

On  the  venter  beneath  and  to  the  side  of  the  vasifon  i 
orifice  is  a  pair  of  spines  arising  from  small  tubercles, 
normally  directed  backward  and  outward,  equal  in  length 
to  the  distal  tibial  spine. 

Second  instar  larva  (fig.  7). — Length,  0.37  to  0.43  mm.; 
width,  0.24  to  0.29  mm.  Broadly  ovate,  dorsum  densely 
rugose,  all  marginal  tubercles  and  spines  wanting  except  2 
cephalic  and  4  anal,    the    three  pairs,  counting    from  the 

1  o  3 

cephalic  region,  giving  the  relative  lengths:    — ,    — ,    -jr-^.- 

Eyes  smaller  and  less  regular  in  outline  than  in  the  first 
instar,  but  distinctly  evident.  Antenna?  greatly  reduced, 
unsegmented,  directed  backward  and  slightly  outward, 
tapering,  reaching  nearly  to  base  of  first  pair  of  legs;  on 
inside  near  base  with  a  distinct  spinelike  projection,  and  on 
basal  portion  with  numerous  roughenings;  legs  almost  rudimentary,  reduced  to  short, 
stotit,  fleshy  processes  without  distinct  segments,  composed  of  a  very  stout,  tapering 
basal  portion,  and  a  comparatively  small,  rounded,  thick  terminal  disc;  the  second 
and  third  pairs  of  legs  on  the  inner  side  at  the  base  with  a  minute  spine.  Mouth 
parts  as  in  previous  stage;  prostomal  plate  anteriorly  indis- 
tinct and  its  pair  of  spines  wanting.  Spines  on  either  side 
of  vasiform  orifice,  both  on  dorsum  and  venter,  as  in  first 
instar.  A  marginal  pore,  on  either  side  of  body  opposite 
base  of  first  pair  of  legs,  and  formed  by  an  upward  fold  of  the 
integument,  becomes  very  evident  in  this  instar. 

Third  instar  larva  (fig.  8).— Length,  0.62  to  0.78  mm. ;  width, 
0.43  to  0.58  mm.     Very  similar  to  second  instar  but  larger; 
the  most  striking  difference  presented  by  the  antenna?,  which 
have    migrated    backward    so    as    to    arise   from  a   tubercle 
slightly  anterior  to  base  of  first  pair  of  legs.     Antenna?  im- 
movable, directed  mesad  for  about  two-thirds  of  their  length, 
and  then  suddenly  doubled  backward  so  that  the  distal  third 
lies  in  the  same  plane  as  the  basal  portion:     Legs  smaller  in 
proportion  than  in  second  instar  and  prostomal  plate  less  de- 
veloped, but  the  marginal  pores  and  anal  cleft  more  fully  developed 
rod  is  seen  often  protruding  from  the  marginal  pores 
3_ 
4.5' 

THE   PUPA. 


Fig.  8.— The  citrus  white 
fly:  Third  larval  instar, 

ventral  view.    Greatly 
enlarged.   (Original.) 

A  waxen 
Relative  lengths  of  the  mar- 


ginal  spines:    -^    A 


The  introductory  remarks  regarding  the  general  appearance  of  the 
larva  apply  with  equal  force  to  the  young  pupa  (fig.  9,  a,  b,  and  c), 
with  the  exception  that  the  pupa  is  larger,  being  nearly  one-sixteenth 
of  an  inch  long,  is  more  easily  seen,  and  on  either  side  of  the  thoracic 

lines  representing  the  outlines  of  the  legs 


region  3  distinct  curvec 


1 1 


[TRUS    WHIT]     FLY:    LIFE    HIS1  0H\     \M»    II  IBI  I 


•;i 


are  ven  distinct.  Aa  the  pupa  becomea  older  il  becomea  thicker, 
more  rounded  and  opaque,  and  the  outlines  of  the  lega  are  obscured 
b)  the  contents  of  the  body.  Ai  the  approach  of  maturit)  a  bright 
red  or  orange  spot  developa  on  the  back,  and  from  three  to  eighl  da}  a 
before  emergence  the  eyes  of  the  adult  become  visible.  A.  detailed 
description  is  as  follows: 

Length,  L.  10  mm  to  1.40  mm;  width,  0.60  mm  to  L.Omm.  Body  broadly  elliptical, 
ihin.no!  raised  from  Leaf  on  vertical  wax  hinge,  color  pale  yellowish-green,  becoming 
more  yellowish  and  thicker  on  approaching  maturity;  thoracic  lobes,  representing  out- 
Lines  of  the  three  pairs  of  Legs,  and  a  Line  extending  from  between  first  two  pair-  of 
ind  from  the  variform  orifice  to  edge  of  body  distinctly  more  yeUo*  ish,  ae  are  also 
the  line*  representing  the  union  of  the  body  segments  although  these  Lasl  are  promi- 
nent.    As  body  thickens  thoracic  kfoes  beco Less  distincl  due  to  body  contents,  a 

brighl  orange  or  red  medio-dorBal  spot  develops 
ai  anterior  end  of  abdomen,  and  Later,  a  few 
days  before  emergence,  the  purple  eyes  of  adull 
become  very  distinct,  as  also  do  the  white  devel- 
oping wing  pads;  rim  of  vasiform  orifice  brown  or 
yellowish.  All  marginal  bristles  lost  excepl  one 
anterior  and  one  posterior  pair  of  minute  bris- 
tles. A  low  medio-dorsal  ridge  or  carina  and 
corresponding  depressions  on  each  side  extend 
from  the  head  to  the  anal  ring,  traversed  by  short 
transverse  ridges  on  the  thorax  and  abdomen. 
terminating  in  a  low  subdorsal  ridge  hardly  per- 
ceptible; from  these  last  numerous  very  line 
granulated  Btriae  radiate  all  around  the  body  to 
the  lateral  margin.  A  short  transverse  ridge 
appears  near  posterior  margin  of  head  with  a 
curved  impressed  line  in  front.  A  minute  brown 
tubercle  at  the  anterior  end  of  the  subdorsal 
carina  is  sometimes  to  be  seen.  From  a  pore  at  the  edge  of  the  body,  between  head 
and  thorax  and  top  of  anal  slit,  issues  a  very  fine,  glistening-white,  curled  thread 
of  waxen  secretion.  These  so-called  "pores"  in  margin  of  the  cephalo-thoracic 
region  are  formed  by  a  slight  upfolding  of  the  body  which  extends  from  margin  to 
cephalo-thoracic  spiracle  and  forms  an  outlet  for  secretions  from  same.  Location  of 
spiraeles  and  respiratory  system  as  already  described  for  aleyrodids.  Legs  and 
antennae  easily  seen  with  high-power  lens.  Antennae  located  as  shown  in  fig.  9, 
partially  concealing  front  pair  of  legs,  apparently  3-segmented  but  division  inl 
ments  not  distinct;  last  segment  as  long  as  other  two  combined,  with  quite  a  number 
of  irregular  annulations;  tip  provided  with  a  stout  spine.  Legs  short,  very  stout, 
especially  the  two  posterior  pairs;  front  legs  projected  forward:  all  without  distinct 
segmentation;  tarsus  very  short,  stout,  and  rounded.  Vasiform  orifice  nearly  semi- 
circular (for  details  and  shape  see  fig.  9,  b). 

Pupa  case. — "White,  firm,  retaining  definite  shape,  and  remains  firmly  attached  to 
leaf  unless  forcibly  detached.     (See  PL  VIII,  fig.  1.) 


Fig.  9.— The  citrus  white  fly:  a,  ventral 
aspect  of  pupa;  b,  vasiform  orifice  of 
same;  c,  margin  of  body  of  same,  a. 
Greatly  enlarged;  6,  c,  highly  magnified. 
(Original.) 


62 


WHITE   FLIES    INJURIOUS    TO    CITRUS    IX    FLORIDA. 


DURATION    OF    STAGES 


LARVAL  QTSTABS 


Data  upon  the  duration  of  the  larval  instars  nave  been  secured  by 
daily  observations  of  over  300  specimens  marked  as  soon  as  the 
young  larvae  had  settled,  supplemented  by  frequent  counts  of  several 
thousand  specimens  in  various  life-history  cages. 

From  these  records  those  included  in  Table  IX  have  been  chosen 
as  representative.  A  study  of  these  will  give  a  very  accurate  knowl- 
edge of  this  subject,  and  will  impress  upon  one  the  considerable 
variation  in  the  duration  of  the  several  instars  of  larvae  hatching' 
at  the  same  time,  feeding  upon  the  same  leaf,  and  consequently  sub- 
ject to  the  same  weather  conditions.  The  data  also  emphasize  the 
retarding  effect  of  cool  spring  and  fall  weather  upon  the  length  of 
larval  life,  although  this  has  not  been  found  to  be  as  great  as  many 
have  thought.  The, period  of  larval  growth  ranges  from  an  average 
of  23  days  during  the  warmest  months  to  an  average  of  30  days 
during  the  cooler  months. 

Table  IX. — Duration  of  larval  instars  of  the  citrus  white  fly. 


Number  of 

Number  of 

Speci- 
men 

Period  of  growth. 

days  in — 

Sum  of 
effec- 
tive 
tem- 

Speci- 
men 

Period  of  growth. 

days  in— 

Sum  of 
effec- 
tive 
tem- 

No. 

In- 

In- 

In- 

No. 

In- 

In- 

In- 

star 
1. 

star 
2. 

star 
3. 

tures. 

star 
1. 

star 
2. 

star 
3. 

tures. 

1 

Mar.22-Apr.26... 

13 

10 

12 

1.044 

33 

Oct.  3-Oct.  27.... 

- 

5 

12 

736 

2 
3 
4 
5 

is 

7 
8 

do 

do 

do 

11 
9 
10 
11 
9 
9 
8 

34 
35 
36 
37 
38 
39 
40 

Oct.  3-Oct.  30 

Oct.  3-Nov.  11.... 

Oet.3-Oct.29 

Oct.  3-Dec.  4 

Oct.  3-Xov.  4 

Oct.  3-Nov.  1 

Oct.  3-Nov.  2 

5 
7 
7 
31 
12 
8 
8 

8 
15 
8 
14 
7 
8 
7 

14 
17 
11 
17 
13 
13 
15 

811 
1,102 

792 
1,644 

922 
843 
868 

do 

do 

do 

June26-Julyl8... 

7 

7 

898 

9 

June26-Julvl9... 

8 

5 

10 

938 

41 

Oct.  3-Nov.  3 

9 

i 

15 

894 

10 

June  26- July  16... 

8 

fi 

7 

813 

42 

do 

11 

7 

13 

894 

11 

June26-July  18... 

7 

6 

9 

898 

43 

Oct.  3-Nov.  1 

8 

8 

13 

843 

12 

June  26- July  20... 

8 

4 

12 

978 

44 

Oct.  3-Nov.  10.... 

7 

4 

17 

1.060 

13 

June  26- July  18... 

8 

5 

9 

898 

45 

Oct.  3-Oct.  31 

8 

8 

12 

828 

14 

June26-July29... 

8 

5 

20 

1,365 

46 

Oct.  3-Nov.  4 

10 

7 

15 

922 

15 

June  26- July  18... 

8 

5 

9 

898 

47 

Oct.  3-Nov.  8 

7 

7 

22 

1.012 

16 

June  26- JuTv  21. .. 

8 

a 

12 

1,015 

48 

do 

7 

10 

19 

1,012 

17 

June  26- July  IS... 

8 

5 

Q 

898 

49 

Oct.  3-Nov.  2 

7 

9 

14 

868 

18 

June  26- July  16... 

7 

5 

8 

813 

50 

Oct.  5-Nov.  1 

7 

7 

13 

783 

19 

June  26-  July  18... 

8 

5 

9 

898 

51 

Oct.  5-Nov.  7 

5 

17 

11 

932 

20 

June  27- July  19... 

7 

5 

10 

902 

52 

Oet.5-Oct.  31.... 

5 

8 

13 

768 

21 

J  une  27- July  20... 

8 

6 

10 

942 

53 

Oct.  5-Nov.  8 

8 

8 

18 

952 

22 

do 

7 

8 

8 

942 

54 

Oct.  5-Nov.  5 

9 

8 

14 

883 

23 

June27-July  16. .. 

7 

5 

7 

777 

55 

Oct.  5-Nov.  1 

8 

6 

13 

783 

24 

J  une  28- J  uly  21... 

6 

6 

11 

938 

56 

Oct.  5-Nov.  3 

9 

8 

12 

834 

25 

June28-Jufy28... 

7 

9 

14 

•    1,220 

57 

Oct.  5-Nov.  5 

8 

9 

14 

883 

26 

June  28- July  18... 

6 

5 

9. 

821 

58 

Oct.  5-Nov.  1 

10 

6 

11 

783 

27 

J  une  29- J  uly  27... 

5 

4 

19 

1,141 

59 

Oct.  5-Nov.  19.... 

11 

34 

died. 

28 
29 

Julv28-Aug.l8... 
Sept.  28-Nov.  14.. 

5 

7 

4 
10 

12 
30 

866 
1,365 

60 

Oct.  5-Oct.  31.... 

6 

8 

13 

767 

30 
31 
32 

Sept.30-Oct.25... 
Sept.30-Oct.  23... 
Oct.  l-Oct.21 

7 
6 

7 

6 

7 

9 

12 
10 

7 

•  780 
727 
635. 

Aver- 
age.. 

(June26-Aug.  18. .. 
\Sept.  28-Dec.  4... 

7.2 

5.4 
28.3 

10.5 
14.3 

945.7 
903.4 

Does  not  include  No.  37 


2  Does  not  include  No.  59. 


VIM. 


Pupa  Cases  of  the  Citrus  and  the  Cloudy-Winged  White  Flies. 


Fig.  l.— Leaf  showing  pupa  eases  of  Aleyrodes  citri;  also  a  few  pupae  and  eggs.  Fig-.  2.— Under 
surface  of  orange  leaf,  showing  heavy  infestation  by  citrus  white  fly.  Fig.  3.— Leaf  showing 
pupa  eases  of  A.  n  ubifera.    Note  delicate  structure  as  eonipared  with  those  of  A.  citri.  (Original. ) 


I  II  I     CITRUS    WHIT]     KLY:    LIFE    HISTORY     \M>    HABITS. 


63 


II    I'M 


One  of  the  most  interesting  phases  of  life  historj  studies  has  been 
the  wide  range  in  the  duration  of  the  pupal  stage;  a  range  of  from  13  to 
304  days.  Considering  the  relatively  slight  variation  in  the  Length  of 
larvaTlife,  this  range  among  specimens  passing  into  the  pupal 
stage  at  practicallj  the  same  time  is  remarkable.  In  view  of  the  fact 
that  the  effect  of  this  variation  upon  the  duration  of  life  and  number 
of  annual  generations  will  be  fully  discussed  under  those  headings  and 
brought  out  in  Tables  XVand  XVI 1  and  figure  L 2,  only  a  few  of  the 
large  number  of  records  on  file  are  given  in  Table  X  t<>  illust  rate  this 
range  in  pupal  life  during  different  parts  of  ( he  year. 

Table  X.     Duration  of  pupal  stdgt  of  the  citrus  white  Jly. 


men 

N 

Period  ol  gro^  th. 

Num- 
ber of 
days. 

Sum  of 
effective 
tempera- 
ture^ 

Speci- 
men 
No. 

Period  of  growth. 

Num- 
ber of 

days. 

Sum  of 
effective 
tempera- 

l 

j 

3 

l 
S 

8 

10 

\pr.:;n-M:iv  L3 

A.pr.  30-June  20 

'-Aug.  3 

S  -June  5 

May  L8-July31 

*-Mar.  is 

July  15-July30 

July  L5-Aug.  4 

Aug.  15-Aug.  27.... 
Aim.  L5-Aug.  28.      . 

13 
51 
64 
18 
71 
304 
15 
20 
12 
13 

mi 
2,564 
2,866 

11 
12 
13 
14 
15 
16 
17 
18 
19 
20 

Aug.  15-Sept.  6.... 
Aug.  16-Mar.  18.... 
Aug.  K- .Mar.  20.... 

Aug.  1 7-Mar.  25 

Aug.  18-Sept.  10... 

Aug.  18-Apr.  1 

Sept.  30-Mar.  31... 
Oct.  28- Apr.  19.... 

Nov.  l-Apr.  17 

Nov.  8-Mar.  25 

22 

21  1 

216 

220 

23 

182 

17.! 
167 
137 

5,479 
5,574 
931 
5,752 
4,473 
4.  167 
4,069 
3,256 

602 

SMS 

179 

521 

It  will  be  noticed  that  pupa1  pass  either  a  comparatively  few  or  a 
comparatively  large  number  of  days  in  this  stage  and  that  ordinary 
temperal  ures  and  humidity  do  not  have  the  Dower  to  determine  which 

it  -hall  he. 

LOCOMOTION. 

On  hatching  from  the  egg  the  young  larva  is  provided  with  well- 
developed  legs,  as  shown  in  figure  5,  by  the  aid  of  which  it  crawls 
about  the  leaf  for  several  hours  and  then  settles  and  begins  to  feed. 
Because  of  the  aimless  way  in  which  it  crawls,  frequently  doubling 
on  its  own  course  and  turning  aside  for  the  least  obstacle,  it  travels 
over  a  very  limited  area.  It  is  therefore  improbable  that  the  craw  ling 
larva1  ever  leave  the  leaf  upon  which  they  were  hatched,  unless  carried 
on  the  feet  of  birds  or  insects  or  blown  or  dropped  from  one  leaf  to 
another.  After  settling,  the  larva  does  not  change  its  position  on  the 
leaf,  while  with  the  first  molt  it-  legs  become  vestigial  (see  fig.  7)  and 
unlit  for  locomotion.  Larva4  frequently  move  slightly,  especially 
directly  after  or  during  molting  when  they  merely  describe  an  arc 
of  180°,  using  their  mouth  parts  as  a  pivot.  The  larva  passes  into  the 
pupal  stage  without  materially  changing  its  position  on  the  leaf.  The 
only  time,  then,  during  the  life  cycle  when  the  white  fly  is  capable 
of  moving  about  from  place  to  place  is  during  the  winged  adult  stage 
and  the  crawling  larval  stage. 


64  WHITE    FLIES   INJURIOUS    TO    CITRUS   IN    FLORIDA. 


GROWTH. 


Pronounced  and  striking  growth  in  size  occurs  only  at  molting, 
when  the  soft  flexible  skin  of  the  larva  or  pupa  is  able  to  stretch  before 
assuming  its  normal  rigid  condition.  With  each  successive  molt  the 
larva  greatly  increases  its  horizontal  dimensions,  until  by  the  time  it 
reaches  the  pupal  stage  these  are  about  eighteen  times  as  great  as  in  the 
newly  hatched  larva.  When  first  settled  after  molting  the  larva  is  very 
thin,  papery,  and  transparent,  being  seen  with  difficulty  except  with 
the  aid  of  a  lens,  but  after  feeding  several  days  it  slowly  becomes 
thickened  until,  from  two  to  five  days,  sometimes  longer,  before  molt- 
ing into  the  next  instar,  it  is  decidedly  plump  and  whitish  opaque  in 
color.  Oftentimes  before  molting  the  larva  becomes  very  much 
swollen  as  though  gorged  with  liquid.  This  appears  to  be  an  abnor- 
mal condition,  since  many  that  become  thus  unduly  enlarged  either 
fall  or  die  without  molting.  During  the  increase  in  thickness  follow- 
ing feeding,  there  is  no  increase  in  the  horizontal  dimensions.  On 
the  contrary,  increase  in  the  former  is  secured  at  a  slight  expense  of 
the  latter. 

MOLTS. 

Daily  observations  on  over  300  marked  individuals  from  time  of 
settling  to  emergence  of  adult  have  conclusively  demonstrated  that  the 
larva  passes  through  but  three  instars  *  before  reaching  the  pupal 
stage,  instead  of  four  as  has  been  previously  supposed.  Each  larva, 
then,  molts  or  casts  its  skin  three  times  before  becoming  a  pupa.  The 
process  of  molting  was  first  described  by  Riley  and  Howard  2  and  as 
observed  by  the  authors  is  as  follows : 

In  preparing  for  a  molt  the  insect  curves  the  abdomen  upwards  at  considerably 
more  than  a  right  angle,  moving  it  also  occasionally  up  and  down.  The  margin  of 
the  abdomen  has  at  the  same  time  a  slightly  undulating  motion.  During  these  move- 
ments the  insect  is  shrinking  away  from  the  lateral  margin  until  it  eventually  occupies 
only  about  one-third  of  the  original  lateral  space,  causing  a  distinct  dorsal  and  ventral 
median  ridge.  The  skin  then  splits,  not  on  the  dorsum,  as  would  be  expected,  but 
either  at  the  anterior  end  or  underneath  the  head.  The  head  and  prothorax  are  then 
pushed  out  and  the  skin  is  gradually  worked  backwards  by  means  of  the  abdominal 
motions,  the  portion  already  out  swelling  as  soon  as  it  is  free. 

As  the  insect  flattens  after  molting  it  appears  milky  white,  the  head, 
thoracic  lobes,  and  abdominal  segments  being  more  greenish.  At 
this  time  the  legs,  which  resemble  much  the  prolegs  of  a  caterpillar, 
are  very  active,  and  there  appears  a  pair  of  fleshy  protuberances  more 
or  less  movable,  not  as  large  as  the  legs,  but  apparently  of  the  same 

LThis  agrees  with  the  senior  author's  observations  on  the  greenhouse  white  fly 
(A.  vaporariorum)  and  the  strawberry  white  fly  (A.  packardi),  which  are  the  two  species 
of  the  genus  which  have  previously  been  studied  in  greatest  detail.  Tech.  Bui.  1, 
Mass.  Exp.  Sta.  and  Can.  Ent.,  vol.  35,  pp.  25-35. 

2  Insect  Life,  vol.  5,  p.  223,  1893. 


I  n  i     t  i  i  i;i  >    w  n  I  i  i     i  I  \  :    i  ii  I     E1IST0B1     \M>    UAB1 

Btructure,  which  act  as  sucking  di  k  i"  aid  the  insect  in  reattaching 
itself.  These  protuberances  are  later  withdrawn  so  that  uo  trace  of 
them  remains.  While  becoming  attached  to  the  leaf  the  insect  ma} 
be  seen  occasional!}  i«>  rotate  itself  through  an  arc  <>!'  _'7n  ,  in  the  mean- 
while frequently  raising  and  lowering  the  abdomen.  T!  i  kins 
are  usually  blown  awa^  by  the  breeze  or  fall  Crom  the  leaf  as  soon  as 
molted,  but  uot  infrequentrj  arc  found  partially  pinioned  beneath 
the  bod}  of  the  insects.  Molting  occurs  most  actively  during  hours 
of  high  humidity.  New  ly  molted  Ian  a'  arc  abundant  during  tin-  early 
morning  when  the  humidity  ranges  between  100    and  90  . 

FEEDING    SAB]  is    or    i..\i;\   1:    an  D    PI  P 

As  the  white  flies,  or  Alev  ro<li<la\  belong  to  the  Ilemiptera,  or 
sucking  insects,  the  larva1  and  pupa1  do  not  eat  the  tissue  of  the  leaf, 
hut  insert  their  thread-like  mouthparts  and  suck  the  plant  juices  by 
the  aid  of  a  suction  apparatus  located  in  the  head.  Their  ravages  are 
not  accompanied  by  any  visible  effect  upon  the  leaf  itself,  but  may 
be  detected  by  means  of  the  sooty  mold  which  develops  after  the  fly 
becomes  very  abundant.  Our  only  means  of  estimating  the  amount 
of  sap  taken  up  by  the  insect  is  by  the  amount  of  waste  material,  or 
honeydew,  ejected  by  it.  A  first-instar  larva,  on  being  watched  under 
the  compound  miscroscope  for  20  consecutive  minutes  with  the  tem- 
perature at  90°  K..  was  seen  to  eject  honeydew  -IS  times,  or  an  average 
of  about  10  times  every  5  minutes.  A  pupa  with  well-developed  eye- 
spots,  in  March,  with  the  temperature  at  85°  F.,  ejected  honeydew 
4  times  in  5  minutes.  This  difference  in  the  amount  of  honeydew 
secreted  is  due  in  part  to  the  different  temperatures  at  which  the 
observations  were  made  as  well  as  to  the  difference  in  the  degree  of 
development. 

A  very  interesting  observation  on  the  amount  of  sap  extracted  by 
larvae  and  pupae  of  the  white  fly  has  been  made  by  Dr.  Berger1 
Leaves  with  live  larvae  and  pupae  were  placed  between  glass  plates  so 
that  the  ejected  honeydew  was  collected  on  the  glass.  By  weighing 
it  was  found  that  each  live  insect  had  excreted  about  0.0005  gram  in 
is  hours.  At  this  rate  a  tree  infested  with  1 ,000, 000  white-fly  larvae 
and  pupa1  would  lose  one-half  pound  of  sap  per  day. 

The  Adult. 

The  adult  citrus  white  fly  is  very  sinall,  measuring  only  about  one- 
sixteenth  of  an  inch  in  length,  and  with  a  wing  expanse  of  less  than 
one-eighth  of  an  inch.  The  natural  color  of  the  body,  antennae,  legs, 
and  wings  is  entirely  obscured  by  secretions  of  delicate  white  wax  par- 
ticles, so  that  the  insect  appears  snowy  white  (PI.  IX;  text  fig.  10,  a-i) 

1  Bulletin  97,  Florida  Agricultural  Experiment  Station,  pp.  G3-G4,  1909. 
scs:,o0_r>u]i.  92—11 5 


66 


WHITE   FLIES   INJURIOUS   TO   CITRUS   IX   FLORIDA. 


without  spots  or  traces  of  darker  shades  upon  the  wings.  Only  the 
purple  eyes  are  free  from  the  white  wax,  and  are  in  sharp  contrast  to 
the  color  of  the  rest  of  the  body.  A  detailed  description  of  the  adult, 
by  Riley  and  Howard,  follows: 

DESCRIPTION.1 

9  . — Length,  1.4  mm.;  expanse,  2.8  mm.;  four-jointed  rostrum  about  aa  stout  as  legs; 
joint  1  shortest,  joint  2  longest,  and  about  as  long  as  3  and  4  together;  joint  3  some- 
what longer  than  joint  1  and  a  little  shorter  than  4.  Joint  1  of  the  7-jointed  antennae  very 
short,  as  broad  as  long,  subcylindrical,  slightly  wider  distally ;  joint  2  twice  as  long  as  1, 
strongly  clavate,  and  at  tip  somewhat  broader  thanl,  bearing  3  or  4  short  hairs  arising 
from  small  tubercles;  joint  3  longest,  about  twice  as  long  as  2,  slenderer  than  this  and  with 
a  very  narrow  insertion,  rather  abruptly  stouter  at  apical  third,  corrugated  and  ter- 
minating above  in  a  small  callosity  resembling  a  similar  organ  in  Phylloxera;  joints  4 


^sM^2^m>^^^^^mis^- 


Fig.  10.— The  citrus  white  fly.  Adult,  a,  Male;  b,  claspers  of  male;  c,  female;  d,  ovipositor  of  female; 
e,  side  view  of  head  of  female;  /,  antenna;  g,  enlarged  margin  of  wing:  h,  tarsus  and  claws;  i,  tibia. 
a,  c,  Greatly  enlarged;  b,  d-i,  more  enlarged.    (Adapted  from  Riley  and  Howard.) 

and  5  subequal  in  length,  each  nearly  as  long  as  2,  joint  5  bearing  a  short  spine  ante- 
riorly near  apex;  joints  6  and  7  subequal  in  length,  each  somewhat  longer  than  2,  7  with 
a  stout  spine  at  tip;  joints  4  and  7  somewhat  corrugate  or  annulate  but  less  so  than 
apical  third  of  3.  The  2-jointed  tarsi  about  half  the  length  of  the  tibia,  joint  1  of  the 
hind  tarsus  bearing  6  rather  stout  spines  on  each  side;  joint  2  supporting  at  baee  3 
rather  prominent  claws,  the  middle  one  longest.  Ovipositor  short,  acute,  and  retrac- 
tile. Eyes  divided  into  two  by  a  curved  pointed  projection  from  middle  of  cheek, 
the  upper  portion  being  smaller  than  the  lower  portion.  Wings  clear,  colorless;  costa 
delicately  serrate.  General  color,  light  orange  yellow,  tip  of  rostrum  black,  tarsi  and 
part  of  tibia  orange. 

$  . — The  male  resembles  the  female  in  all  important  respects  except  in  being 
smaller.     Claspers  about  as  long  as  preceding  abdominal  joint,  or  one-fifth  the  length 

1  Riley  and  Howard,  Insect  Life,  vol.  5,  p.  222,  1893. 


Bui.  92,  Bureau  of  Entorrm 


Plate  IX. 


Adults  of  the  Citrus  White  Fly  on  Foliage  of  Orange. 

Fig.  1.— Tender  growth  swarming  with  adults.     Fig.  2.— Leaf  of  same  enlarged.     (Original.) 


THE  CITRUS  WHITE    PLY:    LIFE  HIS!  OBI     \M>    HAB1  i    .  67 

ot  the  abdomen,  curved  *  ■  <  •  1 1 1 1  >   upward  and  inward,  each  bearii  equidistant 

minute  cylindrical  piliferous  tubercles  on  upper  and  outer  e<3  long 

pers,  rather  stouter  al  base,  more  lender  toward  tip,  terminating  in  a  toul  spine 
at  upper  end.  Bead  and  abdomen  with  heavj  tuff  of  wax  soon  after  i  uing  from 
pupa. 

Examination  of  a  large  number  of  antennae  shows  that  the  relative 
length  of  the  antenna]  segments  is  subject  to  slight  variations.  The 
average  relative  lengths  are  about  as  follows: 

Segment       I      2      3       I      5      6      7     Spine, 
spaces  *       10,   24,    13,    L6,    Hi,    18,   22,       3 

Although  they  have  examined  thousands  of  males  both  at  and  for 
some  time  after  emergence  and  as  (hey  occur  at  all  times  throughout 
the  grove,  the  authors  have  oever  been  able  to  observe  males  with  the 
tufts  of  wax  on  head  and  abdomen  mentioned  in  the  above  descrip- 
tion and  illustrated  in  connection  with  its  original  publication. 

l.\l  ERGENCE. 
DESCRIPTION  OF  THE   PROCESS. 

The  emergence  of  the  adult  occurs  soon  after  its  purple  eves  and 
folded  whitish  wings  can  be  seen  distinctly  through  the  pupal  skin. 
About  20  minutes  before  the  pupal  skin  is  ruptured  the  body  of  the 

adult  shrinks  gradually  away  from  it  and  assumes  its  natural  shape. 
This  gradual  shrinking  away  from  the  edges  of  the  pupa,  and  the 
accompanying  thickening  of  the  body,  brings  a  pressure  to  hear  on 
the  pupal  skin  which  causes  it  to  split  from  margin  to  margin  between 
the  thorax  and  abdomen  and  along  the  median  line  from  this 
rupture  to  the  anterior  margin.  Through  the  T-shaped  opening 
thus  formed  the  insect  first  pushes  its  thorax,  then  its  head,  with 
little  apparent  exertion.  The  body  now  projects  almost  perpendicu- 
larly from  the  pupa  case,  as  the  pupal  skin  is  called,  with  the  an- 
tenna1, legs,  and  abdomen  still  in  their  pupal  envelopes.  By  a  series 
of  backward  and  forward  movements  the  antennae  and  legs  are  freed 
from  their  membranes  and  are  in  constant  motion.  The  abdomen  is 
now  so  nearly  out  of  the  pupal  case  that  the  fly  is  practically  free, 
holding  on  only  by  means  of  the  end  of  the  abdomen.  With  a  sudden 
forward  bend  of  the  body  the  legs  are  brought  in  contact  with  the  leaf, 
and  with  their  aid  the  fly  frees  the  rest  of  its  abdomen  and  crawls 
away  rapidly. 

The  period  covered  between  the  time  the  insect  ruptures  the  pupal 
skin  and  the  time  it  becomes  entirely  free  from  the  case  and  is  crawl- 
ing is  from  7  to  10  minutes.  Not  infrequently  Hies  die  during 
emergence. 

1  These  represent  the  spaces  read  on  eyepiece  micrometer  when  1-inch  eyepiece 
and  £-inch  objective  are  used,  and  the  miscroseope  tube  is  drawn  to  100. 


68  WHITE   FLIES   INJURIOUS   TO    CITRUS    IN    FLORIDA. 


CHANGES  AFTER  EMERGENCE. 


Immediately  after  emergence  from  the  pupa  ease  the  adult  differs 
from  the  more  mature  individuals  in  that  the  lemon-yellow  color  of 
the  body  is  not  obscured  by  the  white  waxy  secretion  that  subse- 
quently appeals.  Also  the  wings,  which  appeared  as  crumpled 
whitish  pads  when  the  thorax  Mas  iirst  protruded  from  the  pupa 
case,  have  had  time  only  to  partially  expand.  As  the  fly  crawls  away 
from  the  case  the  wings  are  held  perpendicularly  above  the  back,  but 
as  the  wings  gradually  unfold  and  assume  their  normal  shape  they 
are  lowered  to  their  natural  position.  It  requires  about  7  minutes 
for  the  wings  to  become  straightened  after  the  fly  leaves  the  case, 
and  from  about  14  to  17  minutes  from  the  time  the}^  first  begin  to 
expand.  When  fully  expanded,  the  wings  are  colorless  and  trans- 
parent, with  the  costa  pale  yellowish.  The  powdery  whiteness  so 
characteristic  of  the  flies  as  seen  in  the  grove  gradually  appears  as 
the  wax  glands  secrete  their  particles  of  wax.  In  about  one  and  three- 
fourths  hours  the  wings  and  body  have  become  perfectly  white. 


CONDITIONS   AFFECTING   EMERGENCE. 


Aside  from  that  inherent  influence  affecting  the  development  of  the 
citrus  white  fly  and  determining  whether  the  adult  shall  emerge 
during  the  first  or  second  general  emergence  period,  as  hereinafter 
described  under  u Seasonal  history,''  many  field  observations. made  at 
all  seasons  during  the  past  three  years,  supplemented  by  laboratory 
experiments,  have  emphasized  the  great  influence  which  temperature 
has  on  emergence.  While  a  normal  amount  of  humidity  is  necessary 
for  emergence  to  occur,  it  is  not  so  controlling  a  factor  as  temperature 
during  ordinary  Florida  weather,  as  will  be  shown  later.  Light  also 
seems  to  affect  emergence  under  certain  conditions. 

EFFECT  OF  TEMPERATURE   ON  EMERGENCE. 

Conclusions  drawn  from  field  notes,  supplemented  by  laboratory 
experiments,  show  that  emergence  seldom  occurs  outside  the  range  of 
02°  F.  to  85°  F.,  with  preference  to  temperatures  ranging  from  70° 
to  85°.  During  the  winter  months  of  December,  January,  and 
February,  when  the  average  monthly  mean  is  about  60°  F.,  no  emer- 
gence occurs  except  to  a  slight  degree  during  warm  spells  of  several 
days'  duration.  In  January,  1906,  when  the  average  monthly  mean 
temperature  was  59.6°,  or  practically  normal,  no  flies  were  noted  on 
wing  at  Orlando,  Fla.,  except  in  small  trees  beneath  pinery  sheds 
where  the  temperatures  averaged  several  degrees  higher  than  outside. 
During  late  December,  1908,  and  early  January,  1909,  the  tempera- 
ture had  been  sufficiently  high  to  cause  a  limited  amount  of  new 
growth  to  appear  on  some  trees  in  Orlando,  and  on  January  4  a  com- 
paratively large  number  of  adult  white  flies  were  seen  feeding  and 


'I'll  i    CITRUS   w  i Y  '.    i  1 1  i     mi  om     wn    ii  \i 


depositing  eggs  or  new  •  row  i  Ii  in  a  \  erj  sheltoro<l  place.  The  avi 
mean  temperature  of  the  6  da}  s  preceding  this  observation  wa 
F..  while,  for  tin1  6  days  preceding  these,  when  no  white  flies  were 
on  wing,  the  average  mean  was  about  58.5  F.  Adult  white  flies 
were  not  seen  in  the  laboratory  grove  in  February,  1909,  until  about 
the  20th,  or  until  the  temperature  records  for  the  grove  showed  an 
average  daily  mean  of  about  64.5  .  Ii  is  from  the  above  facts  that 
tin4  lowest  temperature  at  which  emergence  occurs  has  hem  deter- 
mined to  be  about  62°  F.  This  conclusion,  drawn  from  general  field 
observations,  is  strengthened  l>\  emergence  records  kepi  in  con- 
nect ion  with  cage  life-history  work  during  the  period  of  active  spring 
emergence  of  March,  1908,  when  the  monthly  mean  was  71°.  Refer- 
ence to  the  data  contained  in  Table  XI  brings  out  the  fact  thai  while 

Table    XI.     Relation  of  temperature  to  emergence9  of  the  citrus  white  fly. 


Date. 

Range  in 
tempera- 
ture. 

Average 
mean  tem- 
perature. 

Emergence  records. 

No.  i. 

No.  2. 

No.  3. 

No.  1. 

1908. 
Mar.    19 
Mar.   20 
Mar.   21 
Mar.  22 
Mar.   2:5 

°F. 

62  89 

63  90 

.VI  65 

66  90 

°F. 
7.").  S 
76.  5 

70.0 
78.  0 

4 
5 
0 
10 
17 

6 

7^ 

1 

09 

71 

4 

1 
15 
4 

is 
0 
15 
35 

emergence  had  been  going  on  actively  two  days  before  and  after  March 
21,  when  the  average  mean  temperature  was  about  75°  F.,  a  drop  in 
the  mean  temperature  on  the  21st  to  59.5°  F.  practically  prevented 
any  white  flies  from  emerging.  The  1  white  fly  that  is  recorded 
under  Nos.  3  and  4  may  have  emerged  on  the  20th  after  the  daily 
record  had  been  taken.  Such  emergences  are  not  rare  at  this  season 
of  the  year,  as  will  be  shown  later.  Of  2  lots  of  about  100  pupae 
each,  from  which  adults  were  nearly  ready  to  emerge,  1  was  placed 
in  a  refrigerator  at  about  56°  F,  and  the  other  kept  at  room  tempera- 
ture which  ranged  between  70°  F.  and  S()°  F.  while  emergence  was 
taking  place.  Of  those  kept  on  ice,  but  1  white  fly  emerged 
during  the  first  12  hours,  as  compared  with  17  from  pupae  kept 
at  room  temperature.  White  flies  continued  to  emerge  on  3 
consecutive  days  from  pupae  kept  at  the  latter  temperature.  No  more 
emerged  from  the  refrigerated  pupa3.  It  is  therefore  evident  that 
emergence  may  occur  at  as  low  a  temperature  as  56°  F.,  though  very 
rarely. 

That  white  flies  seldom  emerge  after  the  temperature  reaches  85° 
F.  may  be  concluded  from  the  following  facts:  During  the  months  of 
July  and  August,  when  the  average  daily  mean  is  about  82°  F.,  a 
newly  emerged  adult  is  rarely  seen  in  the  grove  after  8  a.  m.     Prac- 


70  WHITE    PLIES    tNJUBIOUS   TO   CITRUS    IN    FLORIDA. 

fcically  all  adults  at  this  season  emerge  between  4  and  7  a.  m.  Thisis 
true  both  in  the  laboratory  and  in  the  grove.  Of  233  white  flies 
emerging  separately  in  vials  in  the  laboratory  during  August,  1907, 
212  emerged  between  3.30  and  8  a.  m.,  and  the  remaining  21,  with 
one  exception,  emerged  between  8  and  9.30  a.  m.  In  the  grove  over 
95  per  cent  of  the  white  flies  emerge  before  7  a.  m.  At  this  time  of 
day  the  temperature  ranges  between  70°  F.  and  85°  F.  During  the 
early  spring,  when  the  daily  maximum  temperature  does  not  usually 
exceed  85°,  emergence  is  not  restricted  to  the  early  morning  as  during 
the  heat  of  summer,  but  occurs  at  all  times  of  the  day.  It  may  also 
be  added  that  like  conditions  exist  in  October  and  November,  but 
because  of  difference  in  seasonal  history,  they  affect  chiefly  the  spotted- 
wing  white  fly. 

EFFECT  OF  HUMIDITY  ON  EMERGENCE. 

Under  normal  Florida  conditions  at  Orlando,  at  any  season  of  the 
year,  the  relative  humidity  rises  to  nearly  or  quite  100  per  cent  by 
from  6  to  10  p.  m.,  and  there  remains  until  about  6  a.  m.,  when  it 
normally  drops  rapidly,  sometimes  to  as  lowr  as  19  per  cent,  though 
more  often  to  from  35  to  60  per  cent.  It  has  already  been  stated  that 
over  95  per  cent  of  the  white  flies  will  have  emerged  before  7  a.  m.  or 
before  the  humidity  has  fallen  far  from  the  saturation  point.  That 
temperature  and  not  humidity  is  the  more  important  factor  governing 
emergence  in  Florida,  can  be  inferred  by  a  comparison  of  the  humidity 
and  temperature  records  of  Table  XIII.  It  so  happened  that  the 
cold  wave  of  March  21,  1908,  was  accompanied  by  a  higher  average 
humidity,  but  the  temperature  and  not  the  humidity  prevented 
adults  from  emerging.  Again,  during  the  spring,  when  the  daily 
maximum  temperature  is  seldom  above  85° — usually  less — emergence 
goes  on  even  at  midday  when  the  humidity  has  dropped  to  as  low  as 
33°.  In  this  connection  attention  should  be  called  to  the  fact  that  the 
humidity  in  the  corked  vials  mentioned  under  the  preceding  heading 
remained  at  about  100  per  cent  throughout  the  greater  part  of  the 
experiment. 

There  are,  however,  times  of  abnormal  weather  conditions  when 
lack  of  humidity  seems  to  play  an  important  part  in  preventing 
emergence.  During  the  month  of  March  there  sometimes  occur  dry 
winds  of  several  days'  duration,  accompanied  by  more  or  less  heat, 
which  seriously  check  emergence,  and,  as  far  as  can  be  determined, 
cause  many  pupsB  from  which  adults  are  about  to  emerge  to  die. 

Two  such  periods  occurred  during  March,  1909,  from  the  3d  to  the 
6th,  and  from  the  25th  to  the  27th,  respectively.  During  these 
periods  the  relative  humidity  was  extremely  low,  on  one  day  dropping 
to  19  per  cent.  For  42  hours  during  the  latter  period  the  humidity 
ranged  below  50  per  cent  and  for  36  hours  above  50  per  cent.     During 


in  I    CITRUS   whim     PLY:    i.i  it    in-  i  m|;\     \Nii    ii  \r.'  7  1 

these  periods  emergence  was  noted  to  be  ^eriouslj  checked  and  at  the 
end  of  t lif  latter  upward  of  30  percent  of  the  pupae  were  dead,  appar- 
ent ly  from  no  ot  her  cause. 

I  i  i  I  <  i    OF  i  I'.ii  i    ON  EMKROI 

During  the  summer  months  light  seems  to  have  an  influence  on 
emergence.  Ai  this  season  emergence  in  the  laboratory  and  •. 
begins  at  about  daybreak.  Observations  made  at  hourly  intervals 
on  the  emergence  of  233  adults,  from  3.30  and  la.  m.  show  that  white 
flies  rarely  emerge  before  this  time.  In  one  instance  <»nl\  about  one- 
third  as  many  white  Hies  emerged  from  pupae  kept  in  the  dark  a>  from 
those  kept  in  the  open,  ;md  their  emergence  was  noticeably  delayed. 
During  the  cooler  months  the  low  morning  temperatures  prevent  the 
white  Hies  from  responding  to  this  apparent  stimulation  due  to  light, 
and  they  emerge  at  various  times  after  the  temperature  has  risen 
sufficiently  high. 

DURATION    OF    LIFE. 

Without  food. — In  none  of  the  experiments  conducted  to  determine 

the  length  of  adult  life  without  food  have  white  flies  lived  longer  than 
30  hours,  and  a  very  large  percentage  has  died  before  the  end  of  24 
hours.  When  confined  on  leaves  of  plants  other  than  those  recognized 
as  food  plants,  life  is  usually  longer  than  this,  but  never  approaches 
the  normal  length.  White  ilies  confined  on  crape  myrtle  in  July  died 
as  soon  .-is  those  kept  in  empty  cages,  but  flies  caged  on  oak.  in  March, 
lived  as  long  as  4  days;  those  on  fig,  in  August,  3  days;  and  on  banana 
shrul),  in  July.  2  to  3  days.  In  all  these  tests  flies  were  placed  only 
on  the  tenderest  growth. 

With  food. — Adult  life  under  normal  outdoor  conditions  averages 
about  10  days,  although  individual  white  flies  kept  in  cages  have  been 
known  to  live  as  long  as  27  days.  Adults  are  so  fragile  and  so  easily 
killed  by  winds  and  heavy  showers  and  by  numerous  species  of  spiders 
and  ants  that  their  duration  of  life  is  at  most  very  uncertain.  Cage 
experiments  during  March,  April,  July,  August,  and  September  show- 
that,  in  the  cages  at  least,  there  is  little  difference  in  the  length  of 
life  at  various  times  of  the  year. 

MATING. 

The  courtship  of  the  citrus  white  fly  has  been  observed  to  begin 
within  2  hours  after  emergence,  and  in  one  instance  even  before  the 
winirs  of  either  male  or  female  had  become  whitened.  There  is  no 
time  in  the  day  when  the  males  can  not  be  seen  courting  the  females. 
The  male  appears  unable  to  locate  the  female  at  a  distance  much 
greater  than  one-fourth  of  an  inch,  according  to  Prof.  IT.  A.  Gossard. 
Observations  made  during  the  present  investigations  show  that  when 
males  and  females  are  placed  in  separate  receptacles  and  separated 


72  WRITE   FLIES   INJURIOUS   TO   CITRUS    IX    FLORIDA. 

only  by  a  very  porous  cheesecloth  they  show  absolutely  do  attraction 
to  each  other.  Mating,  therefore,  is  not  so  likely  to  occur  when  the 
adults  are  scarce,  as  it  seems  to  be  the  result  of  chance  meeting  upon 
the  leaves  rather  than  to  such  a  definite  attraction  as  exists  between 
males  and  females  of  many  moths. 

Upon  detecting  the  female,  the  male  approaches  her  nervously, 
stopping  at  intervals,  especially  as  the  distance  lessens,  and  swinging 
his  body  about  excitedly  in  a  semicircle,  tin4  head  being  used  as  a  pivot, 
his  wings  in  the  meanwhile  opening  and  closing  spasmodically.  While 
no  movement  is  made  by  the  female,  she  is  repeatedly  approached 
from  many  directions  before  coition  occurs.  More  often  the  male  lie's* 
alongside  the  female  and  courts  her  in  this  position,  raising  and  low- 
ering his  wings  as  above  described,  and  raising  and  swinging  his  abdo- 
men from  side  to  side.  During  these  antics  of  the  male  the  female 
remains  quiet,  only  occasionally  flittering  her  wings.  While  males 
may  be  seen  courting  females  at  all  times  of  the  day,  it  is  seldom  that 
one  sees  a.  pair  in  coitu  except  late  in  the  afternoon  and  evening.  Be- 
cause of  the  uniformity  of  color  and  the  ease  with  which  adults  are 
disturbed  and  made  restless  the  duration  of  copulation  can  not  be 
stated  with  certainty,  but  it  probably  lasts  but  a  short  time.  Experi- 
ments to  determine  the  duration  of  fertility  have  thus  far  proved 
unsuccessful. 

OVIPOSITIOX. 
AGE   AT  BEGINNING   OYIPOSITTON. 

Virgin  females  in  confinement  have  deposited  eggs  within  &  hours 
after  emergence.  In  one  instance  35  virgins  deposited  58  eggs  between 
5  and  94  hours  after  emergence  during  summer  weather,  with  the 
temperature  ranging  from  80°  to  92°  F.  However,  even  at  this  tem- 
perature single  females  occasionally  did  not  deposit  eggs  for  over  24 
hours.  Prof.  H.  A.  Gossard  *  states  that  egg  laying  begins  at  from 
18  to  30  hours  after  the  emergence  when  the  temperature  ranges  from 
65°  to  75°  F.  Laboratory  tests  have  shown  that  lack  of  fertilization 
does  not  prevent  a  female  from  depositing  eggs,  but  that  she  will 
readily  deposit  infertile  eggs  until  opportunity  for  mating  presents 
itself. 

PORTION  OF   PLANT  SELECTED. 

If  not  numerous,  the  females  deposit  almost  exclusively  on  the  under 
surface  of  the  leaves,  laying  over  75  per  cent  of  their  eggs  on  the  half 
of  the  leaf  bordering  the  midrib.  It  is  only  when  very  abundant 
and  pressed  for  room  that  they  deposit  eggs  thickly  over  the  entire 
lower  surface  and  more  sparingly  on  the  upper  surface,  the  petioles, 
and  the  stems  of  twigs.  Next  to  the  portion  bordering  the  midrib, 
the  natural  depressions  and  the  curled  margins  of  the  leaf,  especially 

1  Bui.  67,  Fla.  Agr.  Exp.  Sta.,  p.  609,  1903. 


nil     CITRUS    WHIT]     FLY:    mm     HIS']  "i;\     \.\|.    n  viJl  I    . 


7:; 


of  the  bender  growth,  are  favorite  places  for  oviposit  ion,  and  not 
infrequently  as  high  as  l<>  per  cenl  of  the  eggn  are  there  laid,  «'\<-n 
when  ilif  adults  are  not  \n\  abundant.  Although  eggs  m.i\  be 
deposited  along  the  leaf  margin,  it  is  seldom  that  they  arc  laid  on  the 
margin  itself ,  as  is  the  case  with  the  cloudy-winged  white  fly.  Even 
when  n»>t  crowded  for  leaf  space,  the  adults  sometimes  settle  upon  the 
underside  of  young  fruit,  where  they  deposit  eggs  freerj  and  appar- 
ently feed. 


MUI.Y    R  \Ti:    OF   «'\  (POSITION. 


Previous  to  these  investigations  n<>  data  have  been  published  <>n 
the  daily  rate  of  oviposition.  In  obtaining  the  data  given  in  Table 
XII,  the  females  recorded  were  collected  at  random  throughout  the 
grove,  \\  ithont  regard  to  aire,  and,  together  with  males  not  mentioned, 
were  caged  over  leaves  cleaned  of  all  eggs  and  larvae  of  the  white 
fly  and  allowed  to  remain  the  recorded  time,  when  the  adults  were 
removed    and    the    eggs    counted. 

Table  XII.     Daily  rate  of  oviposition  of  the  citrus  white  fly. 


Record 

Number 
Date  deposited.              of 

females. 

Duration 
of  egg 
laying. 

Number 

of  eggs 
depos- 
ited. 

Average 

number 

of  eggs  per 

female 
per  24 
hours. 

Average 

mean 
tempera- 
tun'. 

l 
2 
3 
4 
5 
6 

8 
9 
10 

Feb.  23-24, 1909 14 

Apr.  11-15,  1907 3 

Apr.  20-21, 1909 50 

Apr.  21-22, 1900 40 

June  16-17,  1909 30 

July  17-18,  1907 255 

July  22-23,  1907 ID.') 

July  24-26, 1907 50 

Aug.  17-18,  1907 70 

j! -22.  1908 35 

Flours. 
26 
103 
24 
24 
24 
21 
24 
46 
24 
24 

197 

98 

454 

405 

360 

2. 533 

1,216 

1,331 

Ml.-, 

405 

13 
7.6 
9.1 
10.1 
12 
11.3 
11.6 
13.8 
11.5 
11.6 

°  F. 

74.  5 
68  2 

77.  2 

78.  2 
B2 
82 
85 
B4 
81 
79 

Number  eggs  per  da y  per  female,  grand  average,  11.2. 

The  generally  uniform  results  obtained  in  the  nine  records  when 
the  average  mean  temperature  was  about  75°  F.  or  above,  together 
with  the  grand  average  daily  rate  of  oviposition  for  individual 
females  whose  age  was  definitely  known,  as  shown  in  Table  XIII, 
indicate  that  each  female  normally  deposits  on  an  average  10  or  11 
eggs  a  day.  Varying  degrees  of  temperature  above  a  daily  mean 
of  75°  F.  do  not  correspondingly  increase  the  number  of  eggs 
deposited.  However,  temperatures  below  an  average  mean  of  72°  F. 
(estimated)  have  a  distinct  checking  effect  upon  oviposition,  as  shown 
by  record  No.  2. 

Notwithstanding  the  general  average  number  of  eggs  per  day 
deposited  by  the  females  of  all  ages  in  Table  XII,  and  the  same  for 
the  females  of  known  ages  for  the  total  number  of  days  they  lived. 
in  Table  XIII,  reference  to  the  daily  oviposition  records  in  the  latter 


74 


WHITE   FLIES   INJURIOUS   TO   CITRUS   IN   FLORIDA. 


shows  that  as  many  as  14,  19,  27,  or  even  33  eggs  may  be  deposited 
by  a  single  female  in  one  day.  It  will  also  be  noted  that  much 
variation  exists  between  the  number  of  eggs  deposited  by  several 
different  females  on  the  same  day  and  by  the  same  female  on  suc- 
cessive days  without  any  apparent  reason,  and  that  there  exists  no 
appreciable  difference  between  the  rate  of  deposition  by  virgin  and 
by  fertilized  females. 


T  \  ble  XIII.     Number  of  eggs  deposited  by  single  females 

of  the  citrus  white  fly. 

l-h 

Date  of  lirsi 
daily  record. 

Condition  of  female. 

Daily 

rate  of  oviposit  ion  by  individual  females. 

No. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

1 

Auk.  8,  1907. . 
do 

$  +males  12  hours  old 

8 
5 
3 
5 
5 

19 
19 
9 

12 
13 
1G 

8 
18 

9 
14 
13 
17 
15 
17 
16 
16 

22 
12 
5 
4 
14 
5 
14 
14 

11 
12 
13 

3 

12 

33 

17 

9 

2      1  ."> 

6 
14 

8 

1 

13 
16 

7 
15 

0) 

(») 

0 

14 
15 

1 
6 

?, 

do 

15 
9 
20 
12 
13 
11 
2 

13 
16 
5 
15 
23 
16 
13 

3 

do 

do 

15 
6 

10 
14 
4 
9 

19 
3 
9 

10 
2 
9 

14 

4 

do 

A.Ug.   15,1907. 
do 

6 

*i 

q 

fi 

do 

6 
8 
2 

3 

7 

do 

do 

$  +males  8  hours  old 

4 

8 

do 

i 

Flv 

Daily  rate  of  oviposition  by  individual  females. 

Total 
number  of 
eggs  laid . 

Number 
of  days 
lived. 

Average 
number  of 

No 

13 

14 

15 

,0 

17 

18 

19 

20 

21 

22 

23 

24 

eggs  per 
day. 

1 

92 
104 
206 
112 
179 
211 
146 
144 

v                   11.5 

? 

8 
22 
19 
16 
17 
17 
14 

13 

3 

4 

13 
5 
5 

19 

8 
1 

9 

10 
20 

"3 

27 

5 
2 
11 
11 

14 
3 

14 
2 
2 
6 

12 

o 

10 
3 

(3) 

4 
2 

8 
0 

6 
8 

9 

(2) 

6          1 

(') 

9.4 
6.0 

5 

11.2 

6 

(«) 

I1) 

12.4 

7 

8.6 

8 

10.3 

i  Dead. 

-  Dead;  13  eggs  in  abdomen. 

3  Dead;  18  eggs  in  abdomen. 

Number  of  eggs  per  day  per  female,  grand  average,  10.  3. 


4  Dead;  11  eggs  in  abdomen. 

5  Dead;  7  eggs  in  abdomen. 


The  eight  records  in  Table  XIII  are  selected  from  about  forty 
similar  records  on  file  and  are  considered  as  representing  an  average 
condition  of  oviposition.  Although  the  general  average  of  10.3  eggs 
per  day  throughout  life  for  the  8  females  recorded  in  Table  XIII 
agrees  very  closely  with  the  similar  average  obtained  in  Table  XII, 
there  is  sufficient  evidence  in  the  data  in  Table  XIII  to  warrant 
the  statement  that  the  daily  rate  of  oviposition  for  individual  females 
is  usually  greater  during  the  early  part  of  the  insect's  life  and  de- 
creases with  each  successive  week  of  existence.  Leaving  out  of  con- 
sideration the  first  day,  when  the  flies  had  not  reached  their  normal 
egg-laving  capacity,  a  little  calculation  shows  that  the  average  daily 
deposition  for  the  three  successive  weeks  is  12.8,  8.5,  and  6.1,  respec- 
tively. This  same  decrease  in  the  number  of  eggs  deposited  with 
increase  in  age  is  perhaps  better  brought  out  by  a  study  of  the  number 
of  eggs  deposited  by  the  individual  females  over  5-day  periods. 
Thus  No.  6  averaged  16.2  eggs  per  day  for  the  first  10  days,  but  for 


tin    ri  I  i;rs   win  i  i     PLY:  UF]     mi    i"i:\     \  n :i»    m  \i; 

the  next  5  dropped  to  an  average  of  7.8;  Nos.  I  and  7  Bhowed  a  sharp 
falling  off  during  the  second  5  days.     No.  3  i    an  exception  to  the 
above  statement,  maintaining  an  average  of  from   9.8  to   11.8  < 
per  <l:i\    for  the  first  three  periods  <>!"  5  days  each,  and  during  the 
fourth  period  of  5  days  deposited  as  man}   <  during  the  first 

5  days,  li  will  be  noticed,  however,  that  No.  3  deposited  compara- 
tively few  eggs  during  the  early  part  of  her  life.  In  view  of  the  fact 
that  tin*  average  adult  life  is  only  about  I"  days,  the  higher  rate  of 
deposition  during  early  life  has  an  influence  on  multiplication. 

\i  MB]  B   OF    i  '.'■■    M  POSIT]  D    B"!    SINGLE   iim  \  lis. 

First  mention  of  the  egg-laying  capacity  of  the  citrus  white  fly 
was  made  by  Riley  and  I  low  aid.'  who  based  their  conclusions  on 
the  number  of  eggs  that  could  be  counted  in  the  abdomen  of  the 
females  when  mounted  in  balsam,  and  not  upon  daily  counts  of  eggs 
deposited  by  the  females  throughout  life.  Their  estimate  of  about 
25  eggs  as  the  probable  total  number  of  eggs  deposited  by  a  single 
female  during  lib1  has  been  generally  accepted  by  subsequent  writers, 
none  of  whom  has  ever  placed  the  maximum  nmnber  deposited 
above  this  figure.  The  present  investigations,  however,  have  demon- 
strated that  this  estimate  is  far  too  low  and  that  the  number  of  well- 
developed  e,u,u's  to  be  found  in  the  abdomen  of  the  female  al  any  one 
time  is  not  indicative  of  the  number  of  eggs  deposited  throughout 
her  life.  Females  have  been  known  to  deposit  more  than  this  number 
of  eggs  in  a  single  day.  As  will  be  seen  by  reference  to  Table  XIII,  as 
many  as  211  eggs  have  been  actually  deposited  by  one  female,  and 
should  the  11  well-developed  eggs  found  in  her  abdomen  at  death  be 
added  a  total  of  222  eggs  would  be  obtained.  As  this  female,  No.  0, 
lived  but  17  days  and  others  have  been  known  to  live  28  days,  it  is 
even  probable  that  as  many  as  250  eggs  more  nearly  represent  the 
maximum  egg-laying  capacity  under  most  favorable  condit  ions.  How- 
ever, it  is  seldom  that  a  female  lives  sufficiently  long  to  deposit  her 
full  quota  of  eggs.  With  the  average  length  of  adult  life  curtailed  to 
about  10  days,  the  average  of  149.2  eggs  per  female,  as  shown  in 
Table  XIII,  is  beyond  doubt  high.  An  average  of  125  eggs  per  female 
is  nearer  the  number  of  eggs  deposited  dining  life  in  the  grove. 

ACTIVITY  IN  oyipositiox   DURING   DIFFERENT  PARTS  OF  THE   DAT. 

In  order  to  determine  that  portion  of  the  day  when  eggs  are  most 
freely  deposited  by  females  during  summer  weather,  adults  were 
inclosed  in  a  rearing  cage  over  leaves  from  which  all  previously 
deposited  eggs  had  been  removed,  and  allowed  to  remain  for  a  period 
of  two  hours,  when  the  cage  with  adults  was  removed  to  another  leaf 
and  the  deposited  eggs  counted,  with  results  shown  in  Table  XIV. 

1  Insert  Life,  vol.  5,  j>.  222,  1893. 


76  WHITE  FLIES  INJURIOUS   TO   CITRUS   IN   FLORIDA. 

Ta  b  le  XIV.  — Activity  of  the  citrus  white  Jly  in  oviposition  during  different  parts  of  the  day. 


Time  of  day, 


G  a.  m.-8  a.  in 

8  a.  m.-10  a.  in .. . 

10  a.  m.-12m 

12m.-2p.  in 

2  p.  111.-4  p.  in.... 

1  p.  m.-G  p.  in 

6  p.  m.-s  p.  in 

8  p.  m.-G  a.  in 

6a.  m.-G.  a.  m..  . 


Mean  tem- 

Number 

Percent  of 

perature 

of  eggs 

total  eggs 

for  period. 

deposited. 

deposited. 

°  F. 

82 

20 

2.6 

89 

55 

7.3 

91 

35 

4.7 

92 

65 

8.7 

90 

30 

4 

85 

197 

2G.  1 

81 

248 

32.9 

74 

103 

13.7 

i  81.6 

753 

100 

1  Average  temperature  for  entire  day  of  24  hours;  not  the  average  of  the  8  periods. 

From  the  data  it  will  be  seen  that  while  oviposition  oeeurs  at  all 
times  of  the  day,  nearly  60  per  cent  of  the  eggs  are  deposited  between 
4  p.  m.  and  8  p.  m.,  and  that  oviposition  does  not  cease  on  the  ap- 
proach of  darkness.  The  variation  in  the  number  of  eggs  deposited 
during  the  periods  from  6  a.  m.  to  4  p.  m.  has  little  significance.  It 
was  noted  that  the  least  number  of  eggs  were  deposited  when  the 
bright  sun  fell  directly  upon  the  cage. 

In  further  evidence  of  the  greater  activity  of  oviposition  during 
the  latter  part  of  the  day,  two  other  cages  were  started  on  August  1, 
1909.  One  cage  placed  repeatedly  over  the  tenderest  growth  resulted 
in  698  eggs  being  laid  between  10.15  a.  m.  and  4.15  p.  m.,  as  com- 
pared with  895  eggs  laid  between  4.30  p.  m.  and  7.30  p.  m.  The 
second  cage,  covering  spring  growth,  gave  115  as  compared  with  786 
eggs  deposited  during  the  same  periods. 

Relation  between  oviposition  and  food  supply. — As  the  egg-laying 
capacit}r  of  a  single  female  is  close  to  250  eggs  and  but  25  well- 
developed  eggs  have  ever  been  seen  in  her  abdomen  at  any  one  time, 
it  is  necessary  that  she  obtain  nourishment  sufficient  to  mature  her 
numerous  " potential"  eggs.  There  remain  many  interesting  obser- 
vations and  experiments  to  be  made  on  the  relation  between  oviposi- 
tion and  food  supply.  That  females  deposit  fewer  eggs  when  feeding 
upon  many  of  the  recognized  food  plants  other  than  citrus  than  they 
do  on  the  latter  is  a  subject  of  considerable  interest.  While  adults 
feed  apparently  as  contentedly  upon  new  growth  of  China  trees  and 
umbrella  Cliina  trees,  they  do  not  appear  to  deposit  as  many  eggs 
per  female  on  these  host  plants  as  on  citrus.  The  extremely  small 
number  of  eggs  laid  by  females  swarming  over  new  growth  of  wild 
persimmon  in  June  at  Orlando  is  even  more  astonishing  consideri og 
the  marked  preference  shown  by  the  females  for  this  growth  over  the 
spring  growth  of  orange.  Even  on  citrus  itself  oviposition  is  influ- 
enced by  the  ages  and  corresponding  toughness  of  the  leaves,  though 
not  as  markedly  as  is  that  of  the  cloudy- winged  white  fly.  In  one 
instance  equal  numbers  of  adults  were  confined  on  a  tender  and  an 


THE   CITRU8  WHITE    PLY:    LIFE    HI8TOB1     won  IB1  77 

old  leaf  of  orange  for  i\\<»  hours,  when  the  adults  were  removed  and 
576  eggs  were  found  to  have  been  laid  on  the  tender  leaf  and  bu1  25 
on  the  old  leaf.  Again,  under  practically  the  Bame  condition  364 
Qcrgs  were  deposited  upon  tender  growth  and  l>ui  2  on  ver\  <»l<l  growth. 

do  r  i  ■  wo 

The  difference  between  oviposition  on  tender  August  growth  and 
spring  growth  is  not  as  great  as  this,  though  very  marked,  as  about 
90  per  cent  of  the  third-brood  adults  fly  to  the  new  growth  put  on 
by  the  trees  late  in  duly  and  early  in  August. 

From  the  foregoing  it  is  evident  that  the  number  of  eggs  deposited 
is  strongly  influenced  by  the  nature  of  the  insect's  food.  Females 
confined  in  empty  cages  never  deposit  eggs,  neither  do  those  resting 
upon  thick  hark,  ladders,  or  picking  boxes,  and,  as  has  been  stated 
under  "Food  plants,''  oviposition  is  entirely  cheeked1  when  females 
are  confined  with  leaves  of  nonfood  plants.  This  difference  in  the 
number  of  eggs  deposited  on  various  plants  may  prove  of  value  from 
tlu' standpoint  of  trap  foods,  and  become  a  factor  in  the  control  of 
this  pest. 

PROPORTION    OP   SKXKS. 

Examination  of  thousands  of  adult  citrus  white  flies  at  all  seasons 
of  the  year  has  shown  that  after  a  grove  has  become  well  infested  an 
equilibrium  between  the  proportion  of  males  and  females  is  estab- 
lished from  which  there  is  under  ordinary  conditions  little  variation. 
In  such  groves  it  has  been  found  that  from  60  to  75  per  cent  of  the 
adults  are  females.  Of  the  records  on  file,  about  60  per  cent  give 
percentages  of  60  and  over  for  females,  wdrile  66  to  76  per  cent  are 
more  frequent  percentages  where  adults  are  abundant. 

In  groves  where  the  progress  of  the  white  fly  has  been  very  seri- 
ously and  suddenly  checked  by  natural  or  artificial  causes,  the  pro- 
portion of  sexes  is  subject  to  a  much  wider  variation  and  there  follow 
for  a  time  fluctuations  between  a  predominance  of  males  and  females. 
In  one  such  grove  where  the  wliite  fly  had  been  greatly  reduced  in 
numbers  because  of  the  scarcity  of  adults  of  the  first  brood,  there  was 
a  very  large  percentage  of  males  appearing  with  the  second  brood, 
which  in  turn  resulted  in  the  third  brood  of  90.5  per  cent  females. 
In  a  second  grove,  where  over  99  per  cent  of  the  white  fly  were  killed 
by  fumigation,  the  few  females  of  the  first  brood,  because  of  their 
isolation  due  to  scarcity  in  numbers,  were  forced  to  deposit  mostly 
infertile  eggs,  which  resulted,  in  the  second  brood,  in  a  reduction  of 
females  to  18.6  per  cent. 

Dependence  of  sex  upon  parthenogenesis. — The  proportion  between 
the  sexes  is  largely  and  evidently  entirely  dependent  upon  partheno- 
genesis.    It  has  been  shown  that  infertile  females  deposit  eggs  in  as 

1  Three  hundred  adults  of  A.  citri  confined  on  the  tenderest  spring  growth  of  oak 
for  three  days  deposited  1  egg. 


78  WHITE    FETES    [NJURIOUS    TO    CITRUS    [»    FLORIDA. 

Large  aumbers  and  as  frequently  when  males  are  not  given  access  to 
them  as  do  fertile  females,  and  that  the  adults  developing  from  these 

eggs  are  all  males.  Whether  the  adults  from  fertile  eggs  are  invari- 
ably females  lias  not  been  proved,  although  the  evidence  leaves  httle 
doubt  that  they  are.  If  otherwise,  it  would  be  difficult  to  account 
for  the  fluctuations  in  sexes  mentioned  under  the  preceding  heading, 
or  to  explain  the  great  predominance  of  females  over  males  after  the 
species  has  become  well  established. 

INFLUENCE  OF  WEATHER  CONDITIONS  ON  ACTIVITY  OF  ADULTS. 

During  the  cooler  portions  of  the  year,  when  adults  are  present  on 
the  trees,  very  few  are  seen  Hying  about  from  tree  to  tree  unless 
abundant.  The  morriiiig  and  evening  temperatures  easily  chill  them; 
hence  their  activities  are  confined  to  the  warmer  part  of  the  day. 

However,  after  summer  weather  has  become  established  the  white 
flies  rest  very  quietly  on  the  under  surface  of  the  leaves  during  the 
greater  part  of  the  day.  They  shun  the  bright  sunshine  and  prefer 
leaves  in  shaded  places.  When  exposed  to  the  sun  without  protec- 
tion they  soon  die.  As  the  temperature  falls  during  the  late  after- 
noon, and  especially  after  afternoon  showers  when  the  humidity  has 
risen  to  90°  or  even  to  100°,  the}'  become  very  active,  and  about  4 
o'clock  begin  to  fly  about  from  leaf  to  leaf  and  from  tree  to  tree,  and, 
when  very  abundant,  swarm  in  such  large  numbers  about  the  groves 
and  town  streets  as  to  arrest  the  attention  of  pedestrians,  to  whom 
they  become  at  times  a  source  of  much  aggravation,  becoming  en- 
tangled in  the  hair,  crushed  upon  the  clothing,  breathed  in  with  the 
air  and  causing  choking,  and  flying  into  the  eyes. 

FEEDING    HABITS   OF  ADULTS. 

The  adult  insects,  having  well-developed  sucking  mouth  parts,  feed 
upon  the  plant  juices  in  the  same  maimer  as  do  the  larvae  and  pupae, 
but  with  the  advantages  of  not  being  confined  to  the  same  location. 
They  do  not  leave  any  external  evidence  of  the  feeding  except  on 
very  young  growth,  when  the  feeding  of  a  large  number  of  adults 
frequently  produces  a  crinkling  of  the  foliage. 

It  is  difficult  to  determine  positively  whether  or  not  an  adult  citrus 
white  fly  is  feeding  when  it  is  resting  on  a  leaf  or  stem.  Adults  rest 
contentedly  during  the  warm  portions  of  the  day  upon  the  underside 
of  leaves  of  plants  upon  which  they  have  never  been  known  to  de- 
posit eggs.  Under  these  circumstances  they  even  appear  to  mate, 
and  it  seems  probable  that  they  feed  to  a  limited  extent.  When  on 
one  of  the  principal  food  plants  of  the  species,  however,  it  is  safe  to 
consider  that  adults  feed  wherever  eggs  are  deposited  in  noticeable 
numbers.  It  is  because  of  this  indiscriminate  settling  upon  vege- 
tation upon  which  they  are  not  able  to  subsist,  and  upon  which  they 


CHE  CITBU8  WHITE  PLY:  UPB    BIST0R1     \M>    iiaiu 

never  breed,  thai  the  belief  baa  received  such  an  unfortunatel}  wide 
circulation  among  orange  growers  thai  the  citrus  while  Il\  breeds  «>n 
all  kinds  of  hammock  trees,  Bhrubs,  and  rdless  o 

food  plain,  the  adults  Iced  almost  exclusively  upon  the  undei 
of  the  leaves,  more  rarely  upon  the  fruit,  and  never  upon  the  wood} 
port  ions  of  the  t  ree.  When  new  grow  i  h  is  \  erj  3  oung  and  the  lea  \  e 
have  not  expanded,  adults  often  feed  upon  both  bu r faces  of  the  leaf, 
the  petiole,  and  even  the  tender  shoots,  but  tins  lasts  only  for  a  short 
time.  At  all  seasons  the  newest  growth  is  preferred,  as  indicated 
l>\  the  data  under  the  caption  of  the  relation  of  food  supply  to  owipo- 

Sltion,  and  tin1  portion  of  the  plant  selected  coincides  with  that 
already  discussed  For  oviposition.  It  should  be  noted  here  that  the 
decided  preference  of  the  adults  for  the  new  growth  has  a  checking 
effect,  as  noted  elsewhere,  upon  multiplication,  as  they  are  entirely 
lacking  in  instincts  preventing  over-oviposition 

Multiplication. 

The  relation  of  multiplication  to  food  supply  and  the  restrictions 
upon  multiplication  due  to  overcrowding,  natural  mortality,  drop- 
ping of  leaves  after  freezes,  parthenogenesis,  and  attacks  by  insects 
ami  other  prcdaceous  enemies  and  fungi  will  be  found  treated  else- 
where. It  has  been  estimated  that  not  more  than  5  per  cent,  at  the 
most .  o(  the  eggs  deposited  throughout  the  State  result  in  the  develop- 
ment of  mature  insects.  If  each  female  deposited  her  full  number 
of  eggs  and  all  the  forms  lived,  it  has  been  estimated,  the  progeny  of 
a  single  pair  of  white  Hies  emerging  in  January  would  amount  to 
about  55,000,000,000  in  one  year. 


80 


WHITE   FLIES    I  N.J  I'UIOUS   TO   OITBUS    IX    FLORIDA. 


Length   oi   Life  Cycle. 

Data  concerning  the  duration  of  the  egg,  larval,  and  pupal  instars 
of  the  citrus  white  fly  have  already  been  given,  but  not  in  a  form  readily 
showing  the  relation  to  the  complete  life  cycle.  From  some  of  the 
more  important  and  complete  of  the  life-history  studies  the  data  in 
Table  XV  have  been  arranged  to  illustrate  the  important  points  in 
this  connection: 

Table  XV. — Length  of  life  cyck  of  the  citrus  white  fly  at  Orlando.  Fla. 


Lot  No. 

Eggs  de-    First  fly 
posited,    emerged. 

Last  fly 
emerged 

in  fall. 

First  fly     ,        fl 
in  spring.  emerSea- 

No.  1 

Feb.  23      Apr.  30 
Mar.     3     May     9 
A  nr.    3     May  30 
Apr.  20     June     7 
June  16     July   30 
July    17     Aug.  27 
do  ...   j  Sept.    4 

No. 2... 

No.  3 

No.  4 

M  ar.     18 

No.  5 

No.  6 

Sept.  10 
Sept.  17 
Sept.  21 
Sept.  20 
Sept.  26 

...do 

Sept.  27 
0 
0 
0 

Mar.  16 
Mar.   17 

...do 

Mar.   18 
Mar.  24 
Mar.   23 

Apr.  16 
May  4 
May  1 
May  10 
Apr.  6 
Apr.     15 

Xo.  7 

No.  8 

No.  9 

July    19     Sept.    2 
Julv   26     Sept.    6 
Aug.     1      Sept.  19 
Aug.     3     Sept.  25 
Aug.    8  1  Sept.  19 
Aug.     9     Mar.   30 
Sept.  18  j  Mar.   16 
Sept.  21     Mar.   12 

No.  10... 

No.  11 

No.  12 

No.  13 

No.  14 

Mar.   20 
Mar.  16 
Mar.  12 

May  12 
Apr.  28 
May     10 

No.  15 

Lot  No. 

Least 
number  of 
days  for 
develop- 
ment. 

Largest 
number  of 
days  for 
develop- 
ment^ 

Per  cent 

emerging 

before 

winter. 

Per  cent 

winter- 
ing over 
to  emerge 
in  spring. 

Smallest 
number 
degrees 
effective 

tempera- 
ture for 

develop- 
ment. 

Degrees 
accumu- 
lating 
1  iefore 
spring 
emer- 
gence. 

Degrees 
accumu- 
lating 

before 

last  fly 

emerged. 

No.  1 

67 
67 
57 

48 

100.0 
100.0 

100.  0 

0 
0 
0 

1, 783 

1,885 
1,888 
1,712 
1,725 
1,641 
1,972 
1,815 
1,703 
2.015 
2, 153 
1,  735 
5,825 
4.552 
4,289 

No.  2 

No.  3 

No.  4 

333 

No.  5 

44 

No.  6 

41 

273 

56.9 

30.8 

12.7 

29.8 

5.5 

3.6 

2.7 

0 

0 

0 

43.1 
69.2 
87.3 
70.2 
94.5 
96.4 
97.3 
100.0 
100.0 
100.0 

6,665 

6,504 

6.255 
6,107 

7,619 

No.  7 

No.8 

No.  9 

49 
45 
42 
49 
53 
42 
223 
1711 

291 
286 
288 
248 

255 

276' 

222 
231 

8,253 
S.059 
7,981 

No. 10 

No.  11 

6,654 

6.858 

Xo.  12 

Xo.  13 

5,825  1           7.. "4.5 

Xo.  14 

4,552 

Xo.  15 

172 

4,289            6,100 

From  this  table  it  will  be  seen  that  the  period  of  development  for 
individuals  hatching  from  eggs  laid  upon  the  same  leaf  within  a  few 
hours  of  each  other  is  subject  to  an  astonishing  variation,  ranging 
from  41  to  333  days.  This  variation  is  absolutely  independent  of 
both  temperature  and  humidity  influences.  It  will  be  noted  that 
the  sums  of  effective  temperatures  required  for  the  minimum  dura- 
tion of  immature  stages  for  individuals  developing  from  eggs  de- 
posited between  February  23  and  August  8  vary  from  1,641°  to 
2,153°,  with  an  average  of  1,846°,  which  may  be  regarded  as  very 
nearly  the  normal  for  minimum  development  up  to  the  time  when 


I  ii  I     L'lTHUfc     WHITE   FLY  :  L'OH> 


M 


all  Individuals  winter  over  as  pup©.  Ii  should  also  be  noted  thai 
the  number  of  maximum  degrees  of  effective  temperature  is  more 
Btronglv  influenced  by  the  time  of  year  the  eggs  are  deposited  the 
nearer  the  winter  months  deposition  takes  place  the  fewer  the  <!<■ 
accumulating  before  the  last  fly  emerges.  This  is  due  to  the  equal- 
izing effect  of  the  cooler  winter  temperatun 

This  same  equalizing  effect  of  the  winter  temperatures  upon  the 
length  of  the  life  cycle  for  individuals  developing  from  eggs  laid  on 
September  20  is  brought  out  in  Table  XVI: 

Tab]  e   XVI.     Duration  ofinstars  of  the  citrus  whiU 


[nstar. 

First. 

Second 

Third. 

Pupal. 

cum- 

So. 

Duration  of 
instar. 

Num- 
ber 
of 

days. 

Duration  of 
instar. 

Num- 
ber 
of 

days. 

Duration  of 
instar. 

Num- 
ber 

of 

days. 

Duratiou  of 
instar. 

N'uiii- 

of 

days. 

ber  of 
days. 

1 

2. 
'■'.  '. 

4 

5 

1908. 

10 

10 

Oct.  3-15 

Oct.3-Nov.2. 

!   10 

8 

8 

13 

31 

S 

1908. 
LO-15.. 
Oct.  10-24.. 
Oct.  15-22.. 
Nov.  2-16.. 
Oct.  10  18.. 

5 
14 

7 
11 
8 

1908. 

Oct.  15-27 

Oct.24   \'o\.  id 
Oct.  22-Nov.  4. . 
Nov.  hi  Dec.3.. 
Oct.  L8-29 

12 

17 
13 

17 
11 

Oct.  27- Apr.  28 
Nov.  10-Apr.  17 
Nov.  4-  V  pr.  s  .. 
Dec.3  Apr.  6... 
Oct.29-Mar.26. 

17:; 
1 58 
1 55 
L28 

198 
197 
L88 
190 

17.-, 

From  this  table  it  will  be  seen  that  retardation  in  growth  during 
any  one  instar  does  not  affect  materially  or  show  a  corresponding 
increase  in  the  total  number  of  days  required  for  development  when 
the  individual  passes  the  winter  in  the  pupal  stage.  Also,  that  an 
unusually  Large  number  of  days  spent  in  one  instar  does  not  neces- 
sarily mean  that  the  individual  insect  will  be  equally  backward 
in  the  next  instar.  These  records  of  daily  observation  on  individual 
specimens  from  hatching  to  adult  are  only  5  of  85  similar  obser- 
vations for  the  same  period.     Xos.  2—5  were  insects  on  the  same  leaf. 


SEASONAL  HISTORY. 
Generations  of  the  Citrus  White  V\.\ . 

It  has  been  generally  understood  in  the  past  that  there  are  three 
generations  annually  of  the  citrus  white  fly,  although  Prof.  II.  A. 
Gossard,1  states  that  "four  generations  a  year  doubtless  often  occur, 
but  not  in  sufficient  numbers  to  obscure  three  well-defined  broods 
as  the  rule."  In  the  greenhouses  at  Washington,  Riley  and  Howard2 
found  that  there  were  but  two  generations  annually.  The  life-history 
work  of  the  present  investigations  has  shown  that  while  the  general 


^ul.  67,  Fla.  Agr.  Exp.  She,  p.  612,  L903. 
-  Insect  Life,  vol.  5,  p.'  224,  1893. 
si ;s.-< »°— mil  1.  92—11 G 


82 


WHITE    FLIES    [NJUBIOUS    TO    CITRUS    IN    FLORIDA. 


observations  of  the  past  leading  to  the  statement  of  three  more  or 
less  distinct  periods  of  emergence  are  correct,  the  number  of  genera- 
tions annually  ranges  from  two  to  five,  or,  under  unusually  favorable 

conditions,  from  three  to  six.  In  figure  11  the  maximum  and  mini- 
mum number  of  generations  as  actually  known  to  occur  in  groves 
at  Orlando  during  1907-9  has  been  plotted.  Figure  11  is  based 
upon  the  development  of  individuals  in  rearing  experiments.     The 

generation  between  January  and  March  may  or  may  not  occur, 
according  to  whether  the  winter  weather  is  warm  or  cold,  but  when 
present  is  numerically  insignificant.  The  other  generations  are 
more  confused  than  can    be   indicated    diagrammatic-ally.     As  may 


f2)Af/ltfCH 


fdjMsfY 


(4)  JUAt£7JOLY 

>     ■     < 


fa)/n/G.,ttpr. 


(SjSEPTLOCT 


(3)JUM£,JULV 


(5)4UG.yS£Pr. 


(6)  SEP*,  OCT. 


y     y  v  y  y  y  \y 

3rt.  4th.       5th.        4th.        5tfi.  6/A  3n/. 

*  ADULTS    EMEPGtNG  AT  THtS  Tttf£  ARE  FROM  EGGS  DEPOS/TEO 
GEFOftE    THE  /5t/r.  OF  A  (/GUST. 

Fig  11.— Diagram  showing  generations  of  the  citrus  white  fly.    (Original.) 

have  oeen  inferred  from  data  in  Tables  XV  and  XVII,  the  variation  in 
the  number  of  generations  is  due  almost  entirely 'to  the  length  of  the 
pupal  stage,  which,  as  has  already  been  pointed  out,  is  subject  to 
wide  variation,  the  cause  of  which  can  not  be  traced  to  food,  tem- 
perature, humidity,  or  location  on  the  tree.  The  most  striking 
variation  in  the  length  of  life  cycle,  with  its  effect  upon  the  possible 
number  of  annual  generations,  is  found  among  individuals  developing 
from  eggs  deposited  in  April  and  May.  In  one  instance  eggs  depos- 
ited on  April  20  produced  adults  on  June  5,  July  31,  and  in  the 
following  March.  In  the  main,  each  generation  has  two  more  or 
less  distinct  periods  of  emergence,  as  reference  to  the  data  in  Tables 
XV  and  XVII  will  show. 


in  i     (II  BUS    whim     i  LI  :   BJ  iBOJH  w.    BISTORT. 

Taum    \\  II       /        ;         oj  adult  citnu  white/lie*  <>t  <>ilnml<>,  l 


Record 

lepoa 

\|.Ml 

M 

June 

\                Ited. 

l  is 

i  is 

l    15 

16   11 

,,. 

l 

Mar.  IH 

Apr.  20 
June  i' 
July  17.... 

Jul)  17 

Jul)  19 
July  2(5 
V.ug.  i. 
lug.  8 

(1 
II 
II 

II 
II 
II 
11 
II 
1) 
I) 

0 

(i 
n 

1 

0 
0 
0 
0 

II 
0 

II 

II 

0 

0 

II 

0 

II 
1 

II 
1) 
ii 
ii 
(1 
0 
II 
(1 
(1 
0 

I) 

II 
;.i 
ii 
n 
ii 
i» 

0 
0 

n 
ii 
(i 

0 

II 

i 

50     1 

II 

0 

II 
II 
II 
II 
II 
II 
II 
(1 

28.6 

(1 
ii 
(i 
ii 
n 
n 
ii 
n 
il 
ii 

n 
n 
ii 
n 

! 

0 
0 

ii 
n 
i) 
(i 

ii 
n 
ii 
ii 
ii 
ii 
ii 
0 
n 

'I 

ii 

7 
B 

'.' 

10 

1 1 

ii 
ii 
ii 
ii 
n 
ii 
ii 
i) 
ii 

n 
o 
n 
n 
ii 

12 

ii 

13 

14 

18.... 

Sept.  21.... 

ii 
i) 

Record 

September. 

October  to 

March. 

March. 

April. 

;a  uqiiiMiru. 

1    15 

L6-30 

1-15 

16-31 

L-15 

1    L5 

j 

Feb.  22 

2 

; 



3 

4 
5 

.Mar.  L8-25 0 

Apr.  20 0 

June  16 

0 
(') 

0 

0 

0 

0 

0 
0 

0 
0 

0 

0 

0 
0 

0 
0 

| 

Julv  17 

July  17 

24.4 
23.9 

8.7 

0.4 

6. 9 

1.7 

6.  5 

3.3 

2.7 

0 

0 

0 

300COOC 
OOOOOOO 

43.1 
67.3 
89.2 
64.3 

0 

1.9 

.4 

5.4 

11.1 

0 
0 
0 
0 
0 

0 
0 

0 
0 
0 

0 

(1 

8 

Julv  19. 

0 

9 

Julv  26.... 

0 

ii 
0 
0 
0 

0 

10 

0 

11 

Aug.  8 

12 

Aug.  9 

98.  7 
38.  3 

1.3 
16.8 

47 

0 
14.9 

11.7 

0 
0 
0 

0 

13 

14 

Sept.  18 

Sept.  21 

0 
0 

0 

0 

0 
0 

1  This  table  is  introduced  to  demonstrate  the  two  emergence  periods  for  individuals  developing  from 
eggs  deposited  at  the  same  time.  It  is  not  intended  to  represent  the  abundance  of  adults  at  different 
times  of  the  year.    Figures  represent  percentages. 

-  only  one  fly  survived  to  winter  over. 

3  One  fly  emerged  July  30.  Leaf  was  broken  off  on  same  day.  Development  of  flies  indicated  that  at 
lea>t  50  percent  would  have  emerged  during  August. 

This  makes  it  possible  for  adults  emerging  during  the  first  period 
to  deposit  eggs  for  a  second  generation,  a  portion  of  the  adults  of 
which  (first  brood)  will  emerge  at  the  time  of  the  second  emergence 
period  (second  brood)  for  the  first  generation,  while  a  large  proportion 
of  the  remaining  individuals  on  the  leaf  to  all  appearances  remain 
stationary  in  their  development,  though  actively  secreting  honeydew, 
until  the  approach  of  the  first  emergence  period  of  the  second  genera- 
tion started  by  the  second  brood  of  the  first  generation,  when  they 
rapidly  mature  and  emerge  with  this  brood.  However,  this  double- 
brooded  character  of  each  generation  up  to  and  including  generations 
started  in  early  August  does  not  obscure  the  three  well-defined 
" broods"  of  adults,  to  be  discussed  under  "Seasonal  fluctuations  in 
the  numbers  of  adults  or  so-called  'broods,'"  but  shows  that  the 
adults  appearing  during  the  three  general  emergence  periods  do  not, 
strictly  speaking,  represent  a  single  brood  of  one  generation,  but 
different  broods  of  different  generations.     By  far  the  greater  number 


84 


WHITE   FLIES   INJURIOUS   TO    CITRUS   IN    FLORIDA. 


of  wintering-over  pupae  belong  to  the  fourth,  fifth,  and  sixth  genera- 
tions, with  the  last  two  most  abundantly  represented.  The  number 
of  third-generation  pupae — or  second  generation  should  the  first  gen- 
eration in  figure  11  not  occur — to  winter  over  is  insignificant. 

Seasonal  Fluctuations  in  the  Numbers  of  Adults  or  so-called  "Broods." 

During  winters  of  unusual  mildness  there  is  a  tendency  for  con- 
tinuous breeding,  and  adults  in  varying  numbers  can  be  found  on 
the  wing  at  different  times,  but  these  are  as  a  rule  too  few  in  number 
to  be  of  importance  in  effecting  the  general  seasonal  history  of  the 
citrus  white  fly.  With  the  exception  of  the  limited  number  of  larva? 
developing  from  eggs  deposited  by  these  unseasonal  adults,  the 
white  fly  passes  the  winter  in  the  pupal  stage.  The  first  general 
spring  emergence  of  adults  begins  after  the  daily  mean  temperatures 
have  risen  to  about  65°  F.,  which  at  Orlando  in  1909  was  about  Feb- 
ruary 20. 

There  are  three  periods  throughout  the  year  when  adult  citrus 
white  flies  are  so  much  more  abundant  than  at  other  seasons  that  it 
is  generally  said  there  are  three  broods  of  white  flies  each  year, 


reefWAfty 

M/I/KH 

JPRtL 

m*r 

JUH£ 

JULY 

AUGUST 

XPrTMBC* 

ocroect? 

NOV£M8£/t 

DEC£Ma£* 

l-IS 

16-20 

1-15 

16-31 

/-/S 

16-30 

l-IS 

16-31 

1-/5 

16-30 

/-IS 

/e-3/ 

/-/s 

/6-3/ 

/-/s 

/6-30 

/-/s 

/e-3/ 

/-/s 

/6-30 

/-/s 

/6-3/ 

r 

"• 

SC 

/ 

\ 

V 

N 

/ 

\ 

/ 

s 

^S 

s 

<s 

v_ 

S 

Fig.  12.— Diagram  showing  abundance  of  adults  of  the  citrus  white  fly  at  Orlando,  Fla.,  throughout 

1909.    (Original.) 

although,  as  already  noted  under  the  subject  of  generations,  the  term 
brood  in  this  case  is  somewhat  misleading.  The  dates  at  which  these 
adults  appear  is  subject  to  such  variation  in  groves  in  the  same 
county,  town,  or  even  on  individual  trees  of  the  same  grove,  that  no 
accurate  statement  of  the  dates  between  which  the  broods  occur 
throughout  the  State  as  a  whole  can  be  made.  The  authors,  there- 
fore, have  chosen  to  follow  the  history  of  the  white  fly  in  a  single 
grove  at  Orlando  during  the  season  of  1909  as  a  specific  example,  as 
a  basis,  and  present  in  figure  12  a  curve  representing  the  abundance 
of  adults  throughout  that  season.  In  all  its  essential  features  the 
curve  is  regarded  as  representing  the  appearance  of  adults  in  any 
grove,  when  it  is  remembered  that  variations  of  from  one  to  three 
or  four  weeks  may  occur  in  the  appearance  of  the  broods. 

While  it  is  generally  believed  that  adults  appear  earlier  in  the  spring 
throughout  southern  Florida,  it  is  a  fact  that  there  is  very  little  dif- 
ference in  time  of  emergence  between  that  and  the  central  portion. 
Emergence  throughout  the  northern  portion  of  the  State  is,  according 
to  the  season,  from  one  to  four  weeks  later  than  in  the  central  and 


l  mi     «  i  I  i;i  s   win  i  i     i  i  \  :    ■  i  \   o»  \i.    BISTORT. 

southern  portions.  Prof.  II.  A.  Gossard  has  Btated  thai  at  Lake 
City  in  L902  \\  hite  flies  began  to  appear  do  earlier  than  April  I  I,  and 
continued  to  appear  until  late  in  May,  although  the  majority  <>f  them 
emerged  during  the  latter  half  of  April,  while  in  L903  the  same  I 
produced  adults  as  early  as  March  12,  or  but  one  week  later  than 
groves  al  Orlando  and  Palmetto.  While  the  spring  brood  of  adults 
nl  Orlando  in  1909  had  begun  to  emerge  as  early  as  February  20  and 
had  reached  their  height  and  begun  to  decline  by  March  27,  on  the 
latter  date  in  St.  Augustine  only  5  per  cent  of  the  pupffi  had  devel- 
oped the  eyes  of  the  adult  and  practically  no  adults  had  emerged. 
Professor  <  rossard  also  is  authority  for  the  statement  that  at  "Tampa, 
.')()  to  40  miles  north  oi'  the  Manatee  section,  the  spring  brood  of 
white  flies  has  in  some  seasons  preceded  their  appearance  about 
Bradentown  and  Manatee  by  two  weeks."  By  June  18,  1909,  more 
than  twice  as  many  adults  of  the  second  brood  had  emerged  al 
Manatee  as  at  Island  Grove  about  125  miles  north  in  Alachua  County, 
while  by  July  7  of  the  same  year  the  white  fly  in  a  grove  at  Alva  in 
Lee  County  was  no  further  advanced  than  at  Orlando. 

From  the  curve  in  figure  12  it  will  be  noticed  that  there  are  two 
periods  of  about  three  weeks  during  the  summer  between  the  broods 
when  adults  are  comparatively  very  scarce.  While  reference  to 
Table  XVII  shows  that  a  few  wintering-over  individuals  continue 
to  emerge  as  late  as  early  May,  the  period  between  the  first  and  sec- 
ond broods  of  adults  is  exceptionally  free  from  adults  of  the  citrus 
white  fly.  This,  however,  is  not  true  of  the  like  period  between  the 
second  and  third  broods  as  before  this  time  the  generations  of  the 
white  fly  have  become  somewhat  confused,  due  to  variation  in  life 
cycle,  and  adults  continue  to  emerge  in  appreciable  numbers  through- 
out the  period. 

In  speaking  of  the  entire  citrus  belt,  including  Florida  and  the 
Gulf  States,  the  greater  part  of  the  spring  brood  may  be  said  to 
emerge  during  March  and  April;  the  second  brood  to  emerge  during 
late  May,  June,  and  July,  and  the  third  brood  during  August  and 
September.  It  should  be  noted  here  that  the  greater  part  of  the 
adult  white  flies  appearing  in  October  and  November  in  the  central 
and  southern  part  of  Florida  are  the  cloudy-winged  white  fly,  A. 
nubifera,  although  in  the  northern  part  adult  specimens  of  A.  dtri 
have  been  seen  in  small  numbers  on  the  wing  in  St.  Augustine  as 
late  as  November  15. 


86  WHITE   FLIES   INJURIOUS   TO   CITRUS   IN   FLORIDA. 

THE  CLOUDY-WINGED  WHITE  FLY. 

(Aleyrodes  nubifei'a  Berger.) 
HISTORY. 

Specimens  of  the  cloudy-winged  white  fly  (eggs,  larvae,  and  pupae) 
in  the  collection  of  the  Bureau  of  Entomology  show  that  this  species 
occurred  on  oranges  in  the  United  States  as  early  as  1889.  The 
records  in  connection  with  the  specimens  show  that  it  was  collected 
in  Mississippi  and  North  Carolina  in  1889,  in  Louisiana  in  1890,  and 
in  Florida  in  1895.  Outside  of  the  United  States  it  is  known  to  occur 
only  in  Cuba.  Its  introduction  into  the  United  States  from  Cuba 
does  not  seem  as  probable  as  its  introduction  into  Cuba  from  the 
United  States.  At  present  there  is  no  evidence  concerning  the 
probable  origin  of  the  insect  except  in  the  absence,  so  far  as  is  known, 
of  other  food  plants  than  citrus,  which  would  seem  to  indicate  the 
introduction  of  the  insect  with  its  only  known  food  plant.1 

Several  writings  on  the  citrus  white  fly  {Aleyrodes  citri)  have  in  part 
included  the  cloudy- winged  white  fly  (A.  nubifera).  Prof.  H.  A. 
Morgan,2  in  1893,  previous  to  the  publication  of  the  original  descrip- 
tion of  Aleyrodes  citri,  briefly  described  the  egg  of  Aleyrodes  nubifera 
and  figured  it,  the  description  of  the  pupa  and  adult  given  at  the 
same  time  evidently  being  based  on  specimens  of  A.  citri.  The 
species  to  which  Prof.  Morgan  referred  the  specimens  was  Aley- 
rodes citrifolii  Riley  MS.  The  original  description  of  the  citrus 
white  fly,3  while  unquestionably  defining  the  species  generally  recog- 
nized as  A.  citri,  included  in  part  reference  to  what  is  probably  the 
spotted-wing  white  fly.  In  the  text  the  description  of  the  first 
stage  or  instar  of  the  larva  was  evidently  based  on  a  specimen  of  the 
spotted-wing  white  fly  and  the  illustration  of  the  first  instar  4  was 
also  based  on  tins  species  with,  little  doubt.  One  figure  of  the  pupa  5 
and  one  of  the  pupa  case  6  evidently  were  based  upon  specimens  of 
the  same  species.  In  the  writings  of  Prof.  Gossard  there  are  no 
references  in  the  text  which  evidently  refer  to  the  cloudy-winged 
white  fly,  but  what  is  probably  this  species  is  represented  in  an 
illustration  of  the  first  stage.7 

1  Its  recent  discovery  on  Ficus  nitida,  rubber  tree,  in  greenhouses  at  Audubon  Park, 
New  Orleans,  La.,  points  to  its  possible  introduction  from  India. 

2  The  Orange  and  Other  Citrus  Fruits.  Special  Bulletin  Louisiana  Agricultural 
Experiment  Station,  p.  72,  1893. 

3  Insect  Life,  vol.  5,  pp.  220-222,  1893. 

4  Id.,  vol.  5,  p.  219,  fig.  23,  d. 

6  Id.,  vol.  5,  p.  219,  fig.  23,  h. 
G  Id.,  vol.  5,  p.  219,  fig.  23,  i. 

7  Bulletin  67,  Florida  Agricultural  Experiment  Station,  pi.  2,  fig.  1.  See  also 
Bulletin  88,  pi.  2,  fig.  1,  and  Bulletin  97,  fig.  11,  Florida  Agricultural  Experiment 
Station,  and  Circular  30,  California  Agricultural  Experiment  Station,  pi.  2,  fig.  1. 


Mil     CLOUDY- WINGED  WUITE  FLY:  INJ1  ST 

The   white  ilv    known   as   the  cloudy  winged  white  Ilv  w 
determined  as  specifically  distinct   from  the  citrus  white  fl\  bj    Dr. 
B.  \\ .  Berger  in   1908.     IV.  Berger  has  recently   given  thi 
Its  scientific  name  in  connection  with  a  synopsis  <»!   the   principal 
distinctive  characters  and  illustrations  of  egg  and   larval  and   pupal 
stages.J 

\moi   \T    OF    [NJUBY    m    THE    CLOl   Dl    WINGED    WHITE    FLY. 

The  injury  caused  by  the  cloudy-winged  while  Ilv  is  al  present 
much  restricted  by  several  factors.  In  Florida  the  distribution  of 
this  species  is  limited  as  compared  with  that  of  the  citrus  white  fly. 
Its  food-plant  differences  and  adaptations  air  such  that  orange 
trees2  are  not  as  a  rule  subject  to  as  heavy  infestations  as  by  the 
citrus  white  fly,  although  with  grapefruit  trees  this  situation  is 
usually  reversed.  Most  important  as  a  factor  limiting  the  injury 
from  the  cloudy  winged  white  fly  is  that  when  both  occur  in  an 
orange  grove  the  citrus  white  fly  almost  invariably  predominates 
and  the  cloudy-winced  white  fly  assumes  a  position  of  comparative 
insignificance.  Owing  to  the  difference  in  the  seasonal  history  of 
the  two  species  of  white  fly  this  latter  point  is  not  always  apparent 
to  the  casual  observer.  An  observation  made  between  the  broods 
of  adults  of  the  citrus  white  fly,  or  at  any  time  after  the  middle  of 
September  up  to  December  1,  may  result  in  noting  a  great  pre- 
ponderance of  the  cloudy-winged  white  fly,  leading  one  to  conclude4, 
perhaps,  that  it  is  this  latter  species  which  is  causing  the  most  injury. 
An  examination  of  the  leaves  during  the  winter  months,  when  there 
are  practically  no  adults  of  either  species,  will  probably  show  an 
entirely  different  situation.  In  many  groves  near  Orlando  and 
Winter  Park  in  Orange  County,  Fla.,  both  species  of  white'  fly  are 
well  established  and  practically  have  assumed  their  normal  rela- 
tive positions  in  point  of  numbers.  Examinations  of  leaves  varying 
in  number  from  85  to  400  pinched  at  random  in.  11  of  such  groves 
furnish  data  which  illustrate  the  general  situation  as  regards  the 
importance  of  the  two  species  of  white  fly  under  the  conditions 
mentioned.  (See  Table  XVIII.)  All  the  examinations  were  made 
during  the  winter  months,  using  pupa  cases  and  live  pupae  as  the 
basis  of  the  comparison. 

1  Bulletin  97,  Florida  Agricultural  Experiment  Station  pp.  68-70,  figs.  L2,  11.  L6, 
is.  L9. 

-According  to  the  latest  statistics  available  (Ninth  Biennial  Report  of  Commis- 
sioner of  Agriculture,  State  of  Florida)  there  were  more  than  five  times  as  many  orange 
trees  as  grapefruit  in  Florida,  1,786,944  orange  trees  being  reported  for  L905  as  against 
373,008  grapefruit  trees. 


88 


WHITE   FLIES   INJURIOUS   TO   CITRUS   IN   FLORIDA. 


Table  XVIII.     Comparative  abundance  of  Aleyrodes  citri  and  Aleyrodes  nubifera  in 
groves  infested  by  both  species. 


Grove  Nos. 

Tangerine. 

Grapefruit. 

Orange. 

pefruit  and 

orange. 

Citri  per 

Nubifera 

Citri  per 
leaf. 

Nubifera 
per  leaf. 

Citri  per 
leaf. 

Nubifera 

per  leaf. 

Citri  per    Nubifera 
leaf.        per  leaf. 

1 

44.2 

7.:. 

L.6 

1.4 

2 

33. 2 

4 
14.5 

4.6 

0. 5 

1.2 
.4 
.2 

3 

4 

5 

C)    .. 

8.8 

2.4 

11.2 

21. 

1.1 

1.6 

8 

9 

33 
30 

.56 

7. 

10 

n 

.9 

.2 

.8 

3.7 

Average. 

Per  cent 

siT  7 

3. 6 
13. 3 

3.7 
59.6 

2.5 

40.3 

19.9 

97.7 

.59 
2.3 

16.1 
92.6 

1.3 
7.4 

Owing  to  the  great  attraction  of  new  growth  for  the  cloudy-winged 
white  fly,  which  is  discussed  elsewhere,  the  scarcity  of  new  citrus 
growth  at  certain  seasons  which  causes  concentration  on  water 
shoots,  and  other  factors,  this  species,  when  it  occurs  by  itself  in  a 
tangerine  or  orange  grove,  does  not  as  frequently  as  the  citrus  white 
fly  cause  noticeable  blackening  of  the  foliage  before  the  middle  of 
June.  At  the  end  of  the  season  the  cloudy-winged  white  fly  by  itself 
may  cause  tangerine  and  orange  trees  to  become  as  heavily  blackened 
with  sooty  mold  as  the  citrus  white  fly  when  the  latter  is  at  its  great- 
est abundance.  As  has  been  stated,  the  cloudy-winged  white  fly  is 
more  likely  to  heavily  infest  grapefruit  trees  than  is  the  citrus  white 
fly.  The  cloudy- winged  white  fly  seems  to  be  subject  to  more  exten- 
sive fluctuations  from  year  to  year,  aside  from  the  effects  of  fungus 
parasites,  than  is  the  citrus  white  fly,  and  frequently  after  infesting 
an  orange  grove  for  several  years  fails  to  cause  enough  injury  to 
make  washing  of  the  fruit  necessary  or  to  make  necessary  the  wash- 
ing of  more  than  one-fourth  or  one-third  of  the  crop  each  year. 

As  a  whole,  the  injury  is  not  as  extensive  in  groves  where  the 
cloud}^-winged  white  fly  occurs  alone  as  in  groves  where  the  citrus 
white  fly  occurs  alone.  When  the  two  species  become  well  estab- 
lished, the  former  does  comparatively  little  damage  except  to  grape- 
fruit. The  authors  would  estimate  that  there  are  about  5  per  cent 
of  the  orange  and  tangerine  groves  in  the  State  infested  b}'  the 
cloudy-winged  white  fly  that  are  not  also  infested  by  the  citrus 
white  fly,  and  that  there  are  in  addition  1  per  cent  of  orange  and 
tangerine  groves  infested  by  both  species  but  in  which  the  citrus 
white  fly  has  not  as  yet  attained  injurious  abundance.  The  average 
damage  from  the  cloudy-winged  white  fly  is  estimated  at  about  10 
to  15  per  cent  lower  for  oranges  where  that  species  alone  infests  the 
grove  than  where  the  citrus  white  fly  is  the  species  concerned.     For 


CHE   GL0UD1    WINGED   WHITE    PLY:    DI8TBIBUTK 

injury  bo  grapefruit  the  authors  consider  25  per  cent  a  fair  estimate 
of  the  injury  by  the  cloud}  winged  white  fl}  as  compared  with  about 
K)  or  15  percent  by  the  citrus  white  fly,  The  total  loss  in  Florida 
<liit4  to  the  cloudy-winged  white  fly  is  estimated  bj  the  authors  at 
between  $100,000  and  $125,000  per  .-1111111111  at  the  present  time. 

DISTRIBUTION. 

So  far  as  known  at  the  present  writing  the  cloudy-winged  white  fly 
occurs  in  12  counties  in  Florida.     The  locality  li>i  i^  given  below:1 

Brevard  County:  Mima,  Sharpes,  Titusville. 
I  fade  County:  Miami. 

Billsboro    County:    Riverview,   Thonotosaasa,    ^'  1  >«  >>•  City,    Clearwater,    Dunedin, 
Largo,  Ozona,  Safety  Harbor,  Saint  Petersburg,  Sutherland. 
Manatee  County:  Bradentown,  Oneco,  Palmetto. 

Momoo  County:   Key  West. 

Orange  County:  Geneva,  Maitland,  Ococo,  Orlando,  Oviedo,  Waco.  Winter  Park. 

Palm  Beach  County:  Palm  Beach,  West  Palmbeach. 

Polk  County :  Ajiburndale,  Bartow,  Lakeland,  Winterhaven. 

St.  Lucie  County:  Fort  Pierce. 

Sumter  County:  Wildwood. 

Volusia  County:  Haw  Creek,  Holly  Hill,  Port  Orange,  Pierson. 

Outside  of  the  State  of  Florida  the  only  available  records  of  the 
occurrence  of  the  cloudy-winged  white  fly  are  those  of  the  Bureau  of 
Entomology  in  connection  with  specimens  in  the  collection.  Mr. 
A.  L.  Quaintance  has  identified  as  this  species  specimens  from  New 
Orleans  (1890)  and  Baton  Rouge,  La.  (1891),  Pass  Christian,  Miss. 
( L889),  and  Raleigh,  N.  C.  (1889).  In  a  brief  examination  at  Audu- 
bon Park,  New  Orleans,  in  August,  1909,  the  senior  author  was 
unable  to  find  any  evidence  of  the  presence  of  this  species,  although 
the  citrus  white  fly  was  prevalent  on  citrus  trees,  privets,  and  other 
food  plants. 

As  stated  in  the  footnote  on  page  27,  the  species  occurring  at 
Bakersfield,  Cal.,  in  1907  was  the  cloudy-winged  white-fly.  Owing 
to  the  fact  that  the  insect  is,  so  far  as  known,  confined  to  citrus  as  a 
food  plant  and  only  a  limited  number  of  these  in  an  isolated  location 
were  infested,  the  thorough  measures  adopted  by  the  agents  of  the 
State  commissioner  of  horticulture  met  with  complete  success,  and 
there  is  no  record  of  this  species  occurring  at  present  in  this  State. 

Its  occurrence  in  Cuba  has  already  been  noted,  specimens  having 
been  received  from  Santiago  de  las  Vegas  in  1905. 

The  distribution  of  the  cloudy- winged  white  fly  in  Florida,  so  far 
as  now  known,  is  shown  in  figure  13.     The  territory  included  in  the 

1  The  authors  have  determined  as  Aleyrodes  nubifera  specimens  from  all  of  the 
localities  listed  above  except  the  following,  which  are  listed  upon  the  authority  of 
Dr.  E.  W.  Berger:  Holly  Hill,  Ybor  City,  Bartow,  Clearwater,  and  Safety  Harbor. 


90 


WHITE    FLIES   INJURIOUS   TO    CITRUS   IN    FLORIDA. 


infested  area  is  not  generally  infested,  and  the  same  precautions 
should  be  observed  within  this  area  as  outside  of  it  to  avoid  unneces- 
sary spread  of  the  pest. 

FOOD    PLANTS. 

The  cloudy-winged  white  fly  is  not  known  in  Florida  to  breed 
upon  any  other  food  plant  than  citrus.  It  has  recently  been  dis- 
covered infesting  the  rubber  trees  (Ficus  nitida)  growing  in  the  green- 
houses in  Audubon  Park,  New  Orleans.  Extensive  examinations 
for  possible  food  plants  have  been  made  by  the  authors  and  by 
Dr.    Berger,    and  it  is  reasonably  certain  that  no   important  food 

plant  will  be  found 
in  Florida  citrus- 
growing  sections 
which  will  interfere 
with  the  control  of 
this  species. 

Examinations  of 
prickly  ash  (Xan- 
thoxylum  clava-her- 
culis),  the  most  com- 
mon representative 
of  the  family  Ruta- 
cese  to  which  the 
citrus  belongs,  indi- 
cate that  this  species 
of  white  fly  never 
breeds  on  this  plant, 
regardless  of  the  con- 
dition of  infestation  of  neighboring  citrus  trees.  Reports  of  blacken- 
ing of  the  foliage  of  prickly  ash  by  the  white  fly  in  sections  where 
only  the  cloudy-winged  white  fly  of  the  two  herein  treated  occurs, 
are  doubtless  erroneous  and  probably  based  upon  the  blackening  due 
to  an  aphis  or  to  some  other  insect.  In  addition  the  following  plants 
have  been  examined  under  favorable  conditions  to  determine  if  sub- 
ject to  attack  by  the  cloudy-winged  white  fly,  but  so  far  without 
results : 

China  trees  and  umbrella  China  trees,  cape  jessamine,  privets, 
Japan  and  wild  persimmons,  oaks,  wild  cherry,  guava,  fig,  grape, 
cherry  laurel,  blackberry,  and  magnolia. 


Fig.  13. — Map  showing  distribution  of  the  cloudy-winged  white  fly 
(Aleyrodes  nubifera)  in  Florida.    (Original.) 


SPREAD. 


The  dissemination  of  the  cloudy-winged  white  fly  is  limited  by  the 
same  factors  which  have  been  discussed  as  unfavorable  to  the  suc- 
cessful establishment  of  the  citrus  white  fly.    Aside  from  these  factors 


'Ill  I     CLOUD  Y- WINCED    VVIITT1     PI  A"  :    I  I  l  l      HISTORY     VXD    HABIT* 


91 


ii^  chief  limitation  is  in  its  lack  of  important  food  plants  other  than 
citrus.  Migrations  of  adults  are  not  an  important  factor  in  the  spread 
of  this  white  lly  except  between  adjoining  groves.  Its  spread  through 
out  anewrj  infested  grove  and  to  adjoining  groves  is  perhaps  favored 
by  its  greater  degree  of  attraction  !<>  new  growth.  It  has  been 
observed  frequently  in  newly  infested  groves  thai  it  is  found  to  be 
present  in  \<m\  small  numbers  over  a  considerable  area,  whereas  the 
citrus  white  fly,  when  at  a  corresponding  numerical  Btatus,  would 
be  expected  to  be  more  localized.  Winds  are  doubtless  concerned 
with  the  spread  of  the  insect  from  local  centers,  but,  as  with  the  citrus 
white  fly,  they  are  evidently  a  factor  of  small  consequence  in  spread 
\o  distant  points. 

Flying  insects  and  birds  as  carriers  of  the  crawling  larvae  are  n< 
sarilv  of  little  or  no  consequence  in  the  spread  of  the  cloudy-winged 
white  fly,  as  with  the  species  previously  discussed.  Between  groves 
vehicles  of  various  kinds  are  of  much  importance  in  distributing  this 
white  fly,  as  is  generally  recognized.  Without  doubt  infested  citrus 
nursery  stock  has  been  the  principal  factor  in  the 
spread  of  the  spotted-wing  white  fly.  Nursery 
stock  from  Minis,  Fla.,  is  quite  definitely  known 
to  have  been  the  source  of  this  white  fly  at 
Sharpes,  Fla.  At  the  present  time  it  seems  to 
be  the  most  probable  source  of  this  white  fly  at 
Fort  Pierce,  Palm  Beach,  and  Miami. 

The  species  here  considered  are  apparently  as 
likely  to  be  carried  on  the  person  from  an  in- 
fested grove  as  is  the  citrus  white  fly,  the  degree 
of  infestation  being  equal.  The  same  may  be 
said  of  pickers'  outfits.  The  introduction  of  fungus-infected  leaves 
into  groves  infested  only  by  the  citrus  white  fly  in  connection  with 
the  introduction  of  fungus  parasites  lias  doubtless  assisted  in  the 
spread  of  the  cloudy-winged  white  fly,  but  not  to  the  same  extent 
that  this  has  assisted  in  the  spread  of  the  former  species. 


Fig.  14.— The  cloudy-winged 
while  By:  Eggs.  Greatly 
enlarged,    i  Original.) 


LIFE    HISTOTCY    AND    II A  HITS. 


The  Egg. 


s  from  that 

and  highly 


The  eg£  (fig.  14)  of  the  cloudy-winged  white  fly  diffe 
of  the  citrus  white  fly  in  that  it  is  not  greenish-yellow 
polished,  but  bluish  or  grayish  black  and  roughened  by  a  film  of  wax 
arranged  in  an  hexagonal  pattern.  To  the  unaided  eye  the  eggk 
appear  as  fine  particles  of  blackish  dust  scattered  over  the  leaves 
(PI.  X,  fig.  1).  Because  of  their  dark  color  they  are  more  readily 
seen  on  the  tender  citrus  growth  by  the  average  observer  than  are 
the  eggs  of  the  citrus  white  fly.  When  first  deposited  they  are  not 
blackish,  but  are  dull  white  or  cream  colored  and  under  the  micro- 


92  WHITE   FLIES  INJURIOUS   TO   CITRUS   IN    FLORIDA. 

scope  the  waxy  coating  appears  tinged  with  red.  The  eggs  remain 
pale  for  three  days,  when  about  96  per  cent  turn  black,  the  rest  taking 
sometimes  as  long  as  seven  or  eight  days  to  darken.  Meanwhile  the 
waxy  coating  has  turned  gray.  Because  of  the  dark  color  and  much 
tougher  chorion,  the  eyes  of  the  embryo  are  not  as  easily  seen  as  are 
those  of  the  citrus  white  fly.  The  eggs  are  attached  to  the  leaf  by  a 
pedicel  arising  from  the  proximal  end  similar  to  that  of  A.  citri. 

A  study  of  the  contents  of  Tables  VIII  and  XIX  will  prove  that 
what  has  been  said  of  the  duration  of  the  egg  stage,  variability  under 
identical  temperature  conditions,  and  effect  of  temperature  in  gen- 
eral, regarding  the  citrus  white  fly,  applies  almost  equally  well  to  this 
species. 


THE   t  Id  l>\    w  i  \«,i  I)    whim     i  i.\ 


Mi.    in-  1 1  »i:  \    ami    II  \j;i  i.-. 


f 

o 


■j-  -> 


bO 

c 
5 


- 


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a  d 

3T5 


^a 


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HjflO 


r  r  r  ~  —  :-  r 


coo  cooo 


OOOO  1«  oo 


— rs 


c^_^o  oco  -* 


i£ 


t^rt  t^.o>  co< 


5  —   tr  ;.  S  a 


5  £  CQ  0Q  CQ  O  O 


Bag  S 
boy  ra ■ 

W5^ 


IOOH0  5DH1T    X 


£  2;  £  !_r  i  — -  i 

•   93  OS  r~.   ~   3  03 
~  -'  W  — '  — i  — '  iH 

oi  — •  c-t      a  c-i  <-h 

ok  OS 

—  ~  -■--■■-  z 

<<-><'S^  QQ  QQ  C 


riNfiTfL1;;!-. 


1 

i 

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8. 

o 

s 

€ 

-r  O  O  Z. 


id  oi  co 


ic  >.o  w  >o  io  io  -r 


t-  O  «C   X  io  N  1^ 

t"-  ^f«  CO       cow  c 


tf  lOio-rf 


O  o  co  —  co  —  X 
3C  -r  r-oi  co  '-. 


Ol  Clt-2  iO 

—  ;--  j  2  — 

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X  iQCQ00>-4eQO 

Tl  «  -T  ~.  ■■*  ~ 


N«fL-)CI* 


94 


WHITE    FLIES   INJURIOUS   TO    CITRUS   IN    FLORIDA. 


The  duration  of  the  egg  stage,  however,  is  in  general  slightly  longer. 
As  the  bulk  of  the  eggs  hatch  from  1  to  10  days  later,  a  slightly  higher 
number  of  degrees  of  accumulated  effective  temperature  are  neces- 
sary, and  hatching  is  more  evenly  distributed  though  not  always 
extending  over  a  larger  number  of  days. 

Tho  process  of  hatching,  proportion  of  eggs  that  hatch,  and  the 
effect  of  drying  of  leaves  in  hatching  do  not  appreciably  differ  from 
what  has  been  stated  of  A.  citri;  in  hatching,  however,  the  egg  mem- 
branes split  only  about  one-third  the  length  of  the  egg  from  the  tip 
and  on  one  side  only,  and  on  account  of  the  tougher  chorion  do  not 
shrivel,  but  retain  their  original  form.  Frequently,  after  the  larva 
has  escaped,  the  membranes  spring  back  into  their  original  position, 
thus  causing  the  eggs  to  appear  unhatched;  as  a  rule,  however,  this 
does  not  occur,  and  the  opening  made  by  the 
escaping  larva  does  not  close.  While  no  adults 
have  yet  been  reared  from  larvse  hatching  from 
infertile  eggs,  it  has  been  proved  that  virgin 
females  of  the  cloudy- winged  white  fry  will 
deposit  eggs  and  that  these  readily  hatch  and 
produce  healthy  larvae,  and  the  evidence  in 
case  of  the  citrus  and  greenhouse  white  flies 
leaves  no  doubt  that  adults  resulting  from  in- 
fertile eggs  will  prove  to  be  of  the  male  sex. 

The  Larval  and  Pupal  Stages, 
the  larva. 


Fig.  15. — The  cloudy-winged 
white  fly:  Ventral  view  of 
crawling  larva  of  the  first 
ins  tar.  Greatly  enlarged. 
(Original.) 


The  larva  of  the  cloudy-winged  white  fly 
does  not  differ  in  general  appearance  from 
that  of  the  citrus  white  fly  except  that  it  is 
a  trifle  larger.  With  the  aid  of  the  microscope 
the  lirst  instar  may  be  separated  from  that 

of  A.  citri  b}r  the  possession  of  36  instead  of  30  marginal  bristles. 

No  structural  differences  between  the  second  and  third  instars  of  the 

two    species  have  been  discovered.     Following  is  a  more   detailed 

comparative  description: 

First  larval  instar  (fig.  15).— Length,  0.29-0.32  mm. ;  width,  0.19-0.22  mm.  Similar 
to  the  corresponding  instar  of  A.  citri,  but  differing  in  being  proportionately  broader, 
in  possessing  18  instead  of  15  pairs  of  marginal  bristles,  and  in  developing  soon  after 
settling  a  marginal  irregular  wax  fringe  eventually  equaling  in  width  the  length  of 
the  marginal  spines.     Relative  length  of  marginal  spines  as  follows: 

Pair      A_     A    A.     AAA,    AAA 
Spaces    10.5'    7.5'    10.5'    8.5'    7. 0'    5.5'    6. 0'    5.  o'    6.0 

Pair     AAAAAAA_A   _A. 

Spaces    5.0'   5. 0'   5.  o'   5. 0'   5.0    6.5'    15.5'    6.5'   15.5* 


Til  !•:    i  l  .ui   l>\    WINGED    WHIM.    I  l.N  :    LIFE    HISTOID     \M»    HABITS. 


Tli 


relative  lengths  and   location  of  other    pine  ol  the  body  do  not  diffei 


.si in i hi i-  spines  on    I   citrt,  neither  do  there  appear  difference   in  tl 
antennae,  '•  »nn  orifice,  or  mouthparl    when  examined  und 

objective.    Particles  of  wax  Becretions  are  found  in  varj  ing 
amounts  on  the  ventral  surface,  sometimes  in  such  abun- 
dance as  i<>  make  microscopic  examinations  difficult. 
S    ond   larval    instar,     Length.   0.42-0.51    mm.:    width 


-   IMI. 

a  one 


in--  of  the 
sixth  Inch 


0   18  0  .:.    mm. 


Except    in 


I >< lint   of   size 
have 


difference 
•n  discov- 
ered between  this 
and  the  correspond- 
ing instar  of  .  1 .  cilri. 
Third  larval  instar 
(fig.  L6). — Length, 
0.66  0.9mm.;  width, 
0.  18  0.68  nun.  Ex- 
cept in  si/.c  no  differ- 
ences have  been  dis- 
covered between  this 
and  the  correspond- 
ing instar  of  -1 .  cilri. 


Fig.  16.  The  cloudy-winged 
white  fly:  Ventral  view  of 
crawling  larva  of  the  third 
Instar.  GreaUy  enlarged. 
(Original.) 


Fie.  17.— The  cloudy-winged  white  fly. 
Pupa:  a,  Ventral  view;  b,  enlarged  vast 
form  orifice;  c,  enlarged  margin,  a,  Greatly 
enlarged;  b,  c,  highly  magnified.  (Origi- 
nal.) 


tin-:   PUPA. 


Iii  general  appearance  the  pupa  of 
the  cloudy-winged  white  fly  (fig.  17,  a, 
h,c)  resembles  very  closely  that  of  the 
citrus  white  fly.  No  striking  structural  differences  have  been  dis- 
covered between  them.  They  are,  however,  very  distinct,  and  one  who 
has  examined  them  carefully  can  readily  separate  them  without  the  aid 
of  a  lens.  The  most  important  differences  are 
in  the  larger  size  and  thinner  and  flatter  appear- 
ance of  the  pupa  of  the  cloudy-winged  white 
fly.  The  difference  in  outline  is  shown  in  figs. 
9,  c,  and  17,  c.  Their  skins  are  more  mem- 
branous, making  them  more  delicate  and  easily 
crumpled.  Furthermore,  after  thickening  be- 
fore maturity  they  do  not  develop  the  bright 
red  or  orange  spot  on  the  middle  of  their  backs, 
and  the  wing  pads  and  body  of  the  adult  (fig. 
IS)  are  more  easily  seen.  The  pupa  case  (PI. 
VIII,  fig.  3)  is  much  thinner,  more  membranous, 
and  falls  from  the  leaf  more  readily.  Its  walls 
do  not  remain  rigid  as  do  those  of  A.  citri,  but 
because  of  their  more  delicate  structure  col- 
lapse after  the  emergence  of  the  adult  and  present  the  crinkled 
appearance  shown  in  the  illustration. 


Fig.  is.— The  cloudy-winged 

white-fly:  Dorsal  view  of 
pupa,  showing  adult  insect 
about  to  emerge.  Greatly 
enlarged.    (Original.  I 


96 


WHITE    FLIES   INJURIOUS   TO    CITRUS   IN    FLORIDA. 


DURATION    OF   [NSTAKS. 


Larval  instars. — By  comparing  the  data  in  Tables  IX  and  XX  it 
will  be  found  that  the  larvae  of  A.  nubifera  are  slower  in  maturing 
than  those  of  A.  citri.  While  this  difference  is  not  so  pronounced 
dining  the  warmer  months  of  the  year,  the  total  average  number  of 
days  being  25.9  and  23.1,  respectively,  during  the  cooler  months  it  is 
very  striking,  the  total  average  number  of  days  then  being  56.7  for 
A.  nubifera,  as  compared  with  30.4  for  A.  citri.  In  other  respects 
the  statements  made  on  the  duration  of  the  larval  instars  for  A.  citri 
apply  to  A.  nubifera. 

Table  XX. — Duration  of  larval  instars  of  cloudy^winged  white  fly. 


Number  of  davs 

Number  of  davs 

in — 

Sum  of 

in — 

Sum  of 

Speci- 
men 

Period  of  growth. 

effec- 
tive 

tem- 

Speci- 
men 

Period  of  growth. 

effec- 
tive 

tem- 

No. 

In- 

In- 

In- 

No. 

In-     In- 

In- 

star 
1. 

star 
2. 

star 
3. 

pera- 
ture. 

star  1  star 
1.       2. 

star 
3. 

pera- 
ture. 

1 

June  26- July  19... 

9 

6 

8 

938 

33 

Sept.  30-Nov.  20.. 

8 

15 

28 

1.322 

2 

June27-July20... 

6 

6 

11 

942 

34 

Sept.  30-Xov.  23.. 

11 

12 

31 

1,401 

3 

June27-July21... 

8 

6 

10 

979 

35 

Sept.  30-Dec.  20.. 

11 

14 

46 

1,831 

4 

June  27- July  26... 

9 

7 

13 

1,179 

36 

Sept.30-Dec.  3... 

8 

19 

37 

l.i,7i> 

5 

June27-July  19... 

9 

7 

6 

902 

37 

Sept.  30-Nov.  23.. 

8 

14 

32 

1,401 

.       6 

June27-July21... 

8 

8 

8 

979 

38 

Sept.  30-Dec.  3... 

11 

12 

42 

1,670 

7 

June27-July  17... 

7 

6 

7 

820 

39 

Sept.  30-Nov.  27.. 

9 

9 

40 

1,513 

8 

June27-July  19... 

5 

7 

10 

902 

40 

do 

8 

14 

36 

1,513 

9 

June27-July20... 

7 

6 

10 

942 

41 

Sept.  30-Dec.  3... 

8 

14 

42 

1,670 

10 

do 

7 

6 

10 

942 

42 

Sept.  30-Nov.  23.. 

9 

11 

34      1,513 

11 

June  27- July  21... 

7 

6 

11 

979 

43 

Sept.  30-Dec.  10.. 

8 

15 

48     1,831 

12 

June27-July  19... 

7 

6 

9 

902 

44 

Sept.  30-Dec.  3... 

8 

14 

42  !  1.670 

13 

June28-July27... 

14 

8 

7 

1,179 

45 

Oct.  2-Dec.  7 

10 

9 

47 

1,704 

14 

June28-July29... 

7 

6 

18 

1,260 

46 

Oct.  2-Nov.  10.... 

7 

9 

21 

1,060 

15 

June28-Julv24... 

11 

8 

7 

1,056 

47 

Oct.  2-Nov.  30.... 

8 

23 

26 

1.524 

16 

June2S-July— ... 

9 

21 

...... 

48 

Oct.  2-Nov.  19.... 

9 

10 

27 

1.235 

17 

June28-July  19... 

6 

6 

'  "sei' 

49 

do 

7 

12 

27 

1 ,  235 

18 

June28-July24... 

7 

9 

10 

1,056 

50 

Oct.  2-Nov.  23.... 

8 

9 

33 

1.332 

19 

June29-July  29... 

6 

15 

9 

1,222 

51 

Oct.  2-Nov.  19.... 

7 

11 

28 

1,238 

20 

June29-July24... 

7 

7 

11 

1,018 

52 

Oct.  3-Nov.  27.... 

11 

18 

27 

1,414 

21 

June29-July29... 

8 

8 

14 

1,222 

53 

<>ct.3-Dec.  3 

10 

17 

35 

1,561 

22 

June30-July  30... 

8 

8 

14 

1,229 

54 

Oct.3-Dcc.  7 

10 

16 

40 

1,662 

23 

June30-July  29... 

12 

7 

10 

1,188 

55 

Oct.  3-Dec.  2 

10 

23 

28 

1.536 

24 

Scpt.30-Nov.  1... 

5 

10 

18 

912 

56 

Oct.  3- Dec.  1 

10 

15 

35 

1,510 

25 

Sept.  30-Xov.  20.. 

8 

16 

28 

1.322 

57 

Oct.  3-Dec.  3 

11 

20 

33 

1,561 

26 

Sept.  30-Nov.  30.. 

12 

12 

38 

1,593 

58 

do ; 

11 

20 

31 

1,561 

27 

do 

14 

15 

33 

1,593 

59 

Oct.  5-Nov.  11.... 

9 

11 

18 

1,000 

28 

Sept.  30-Dee.  3... 

12 

23 

32 

1,670 

60 

Oct.5-Dec.  10.... 

66 

died. 

29 
30 
31 
32 

Sept.  30-Nov.  3.  . 
Sept.  3<>-Dec.  3... 
Sept.  30-Nov.  30.. 
Sept.30-Dcc.  3... 

8 
8 
8 
8 

10 
21 
13 
14 

17 
35 

40 

42 

963 
1,670 
1,593 
1,670 

Aver- 
age 
age. 

]june26-.Tuly30... 
(Sept.  30-Dec.  10.. 

8 
9.1 

7.8 
14.4 

10.1 
33.2 

1.D31.7 

Pupal  instar. — That  little  difference  exists  between  the  length  of 
the  pupal  stages  of  the  two  species  of  white  fly  in  question  is  shown 
by  a  comparison  of  the  data  in  Tables  X  and  XXI.  The  minimum 
length  of  the  pupal  stage  (17  days)  will  average  but  a  trifle  above 
that  of  A.  citri.  But  the  maximum  length  is  so  dependent  upon  the 
seasonal  history  that  a  direct  comparison  is  difficult;  this  subject, 
therefore,  is  more  profitably  discussed  under  the  caption  of  seasonal 
history.  What  has  been  said  in  connection  with  the  maturing  of 
specimens  of  A.  citri  passing  into  the  pupal  stage  at  practically  the 
same  time  is  equally  true  of  the  cloudy-winged  white  fly,  A.  nubifera. 


THE  CliOUDl    WINGED    will  1  i     PLY  j    i .  1 1  i     BIBTOftl     \  N  I  >    1 1  \  I ;  i  i    .       97 
Tabu    XXI.     Duration of  pupal  ttage  of  cloudy-wii 


Sp.vi- 

III. 'II 

1 

2 

a 

i 

B 

6 
7 
B 

g 

in 

\iim- 

Perlod  of  gron  th.         ber  of 
days. 

Sum  of 

effective 
tempera 

Hit.-. 

men 

•  .  W  1  1 1 

M  um- 
bel of 

Sum  M 

m      24  June  11.. 

16  June  ii 

M       26  July  19 

is 

24 

094 

7.1 
2,  1H7 

n 
12 
18 

II 
15 
16 

17 
is 
19 
20 

Oct  31    M 
Nov.  1    \i 

\,.\ .  i  i   \i 

\..\  .   20     M    :'.      l 

'. 

M  UP.  .'. 

Dec.  3  Apr.  29 

Dec.  7  \i 
Dec.  ii   " 

i  OS 
196 

128 

lit 
147 

111 

M 

2,702 

Jul)                      

July  18   \n-.  B 

Oct.  9  Oct,  26      

Oct  9  Oct  28      

Oct  9  Oct  :^i        

i; 

IN 

17 
is 

21 

17 

086 

71-1 



519 
662 
166 

Oct  9  Oct  26      

1  It  is  to  be  regretted  thai  the  falling  of  the  leaf  upon  which  Nos.  Sand  6  matured  prevented  gathering 
data  on  the  maximum  length  of  stage  a1  this  season  of  year. 

GROWTH,  MOLTS,  LOCOMOTION,  AND  FEEDING    HABITS. 

Concerning  growth,  molts,  locomotion,  and  feeding  habits,  there  La 
little  to  add  to  that  already  stated  in  connection  with  the  larvae  and 

pupae  of  the  citrus  white  fly.  The  two  species  are  alike  as  regards 
the  number  of  larval  instars  and  in  their  crawling  and  sedentary 
habits.  Their  maimer  of  feeding  is  similar  also,  with  the  exception 
that  when  crowded  the  larvas  of  the  cloudy-winged  white  fly  settle 
freely  upon  the  upper  surfaces  of  shaded  leaves,  where  they  frequently 
reach  maturity. 

MORTALITY  AMONG  LARV.E   AND   PUP.3:. 

Remarks  relating  to  mortality  among  the  larva?  and  pupa?  of  the 
citrus  white  fly  apply  with  greater  force  to  the  cloudy-winged  white 
fly.  This  mortality  appears  to  result  from  the  same  causes  in  the 
latter  as  in  the  former  species.  Life-history  work  has  shown  that 
mortality  due  to  spring  droughts  and  dropping  from  leaves  is  prac- 
tically the  same  for  the  two  species,  but  that  general  mortality 
including  "unexplained"  mortality  is  about  3  per  cent  higher  for 
A.  nubifera.  In  this  last  respect,  however,  observations  throughout 
groves  where  infestation  is  much  heavier  than  on  leaves  used  in  the 
life-history  work,  and  counts  of  forms  on  leaves  infested  with  both 
species  of  fly,  show  that  the  comparative  susceptibility  to  the  influ- 
ences producing  mortality  of  all  kinds  is  often  at  least  twenty  times 
greater  for  A.  nubifera.  This  greater  susceptibility  appears  to  be 
due  not  only  to  the  more  delicate  structure  of  the  larvae  and  pupae  and 
their  need  of  more  room  for  development  because  of  their  larger  size, 
but  also  to  the  adults'  habit  of  crowding  the  new  growth  with  eggs 
far  beyond  its  capacity  for  maturing  the  larvae  hatching  therefrom. 

As  may  have  been  inferred  already  from  statements  upon  the  sub- 
ject of  oviposition,  it  is  this  insatiable  desire  of  the  adults  for  feeding 
and  ovipositing  on  new  growth  that  is  a  most  powerful  factor  lead- 
ing to  the  insect's  control.  While  a  large  amount  of  data  might  here 
86850°— Bull.  92—11 7 


98  WHITE   FLIES   INJURIOUS   TO    CITRUS    IN    FLORIDA. 

be  presented  illustrating  the  disastrous  effect  on  the  species  resulting 
from  overcrowding,  the  data  itself  would  differ  in  no  respect  from 
that  already  presented  under  the  general  consideration  of  A.  citri. 
Nevertheless,  there  is  a  great  difference  in  the  extent  and  practical 
bearing  of  this  mortality  among  the  immature  forms  of  the  two 
species. 

The  Adult. 

The  adult  of  the  cloudy-winged  white  fly  is  similar  to  that  of  the 
citrus  white  fly,  but  is  at  once  separated  from  it  by  the  dark  spot 
or  shading  on  the  outer  portion  of  the  upper  wings  (PL  X,  fig.  1). 
Except  for  the  further  fact  that  the  female  is  appreciably  more  robust 
the  adults  of  both  species  are  structurally  much  alike.  The  antennae 
of  A.  nubifera  are  not  as  highly  corrugated  as  those  of  A.  citri,  but 
possess  a  terminal  spine  over  three  times  as  long  as  that  of  A.  citri. 
The  eyes  of  A.  nubifera  are  more  nearly  divided  iir  many  instances 
than  those  of  ^4.  citri,  although  tins  is  a  character  subject  to  variation 
in  both  species. 

On  nearly  all  features  of  life  history  and  habits  this  species  closely 
resembles  the  citrus  white  fly,  and  these  subjects  are  therefore  dealt 
with  in  a  comparatively  brief  manner.  The  principal  points  wherein 
the  cloudy-winged  white  fly  differs  from  the  citrus  white  fly  may 
be  stated  summarily  as  follows:  It  is  more  closely  restricted  to  citrus 
for  its  food  supply  as  well  as  in  oviposition;  it  shows  a  more  strongly 
developed  tendency  to  feed  and  deposit  eggs  on  new  growth;  its 
arrangement  of  eggs  and  preferences  for  certain  sections  of  leaves 
for  ovipositing  are  characteristic,  and  it  is  slightly  less  prolific.  Its 
apparent  restriction  to  citrus  as  a  food  plant  has  been  discussed  under 
the  subject  of  "Food  plants."  Its  strong  preference  for  new  growth 
results  in  a  situation  which  can  be  taken  advantage  of  in  the  con- 
trol of  the  pest  by  the  pruning  of  water  shoots. 

The  age  at  which  oviposition  begins  and  the  activity  in  oviposition 
during  different  parts  of  the  day  are  the  same  as  for  A.  citri.  The 
females,  however,  when  not  abundant  deposit  more  readily  along  the 
outer  margin  of  the  under  surface  of  the  leaf  and  along  the  edge 
and  upper  surface,  and  not  so  freely  along  the  midrib  as  is  the  case 
with  A.  citri.  Not  infrequently  90  per  cent  of  the  eggs  will  be 
deposited  on  the  outer  portion  of  the  leaf  wliile  many  are  laid  on  the 
edge  of  the  leaf  itself,  from  which  they  often  project  perpendicularly. 
The  depositing  of  eggs  on  the  leaf  margin  and  on  the  upper  surface 
is  peculiar  to  A.  nubifera  and  is  not  the  result  of  overcrowding.  A 
count  of  4,000  eggs  on  nine  moderately  infested  leaves  showed  that 
8  J  per  cent  of  the  eggs  were  laid  on  the  edge  of  the  leaf,  86.8  per  cent 
on  the  lower  surface,  and  5.1  per  cent  on  the  upper  surface.  When 
adults  are  very  numerous  both  surfaces  of  the  leaves  of  tender 
growth  and  the  petioles  and  shoot  stems  are  thickly  covered  with 


Bureau  of  E' 


P 


The  Cloudy-Winged  and  Citrus  White  Flies. 

Fig.  1.— Adults  of  the  cloudy-winged  white  fly.  .4.  nubifera,  showing  cloud  or  spot  at  tip  of 
wings,  and  many  eggs  scattered  about.  Fig.  2.— Larva-  and  pupa-  or"  both  the  citrus  white 
fly  and  the  cloudy-winged  white  fly  killed  by  fumigation.  During  life  they  are  nearly  trans- 
parent and  seen  only  with  difficulty.     Note  eggs  of  A.  citri  along  midrib.     |  Original.) " 


Ill  B  CLOUDY- WINGED  V Y  I  LTF1     n  [8TOR1     \  M»    II  IB 


eggs.     While    the   citrus  white   ll\    « !«•  j »< »-i t ^   ber   i  without    any 

definite  arrangement,  the  cloudy-winged  \s  1 1 i i  «*  fly,  like  many  other 
species  of  AJeyrodes,  verj  frequently  lays  hei  of  various  Bizes, 

and,  as  she  is  less  restless  while  feeding,  has  b  tendency   to  dej 
her  eggs  in  groups.     This  arrangement,  together  with  the  difference 
in  color,  makes  easy  the  separation  of  bhe  two  species. 

Reference  to  the  data  in  Table  XXII.  especially  when  compared 
with  thai  in  Table  XII,  shows  that  the  daily  rate  of  ovipositioE  for 
tin*  cloudy-winged  white  fly  is  slightly  less  than  for  the  citrus  white 
fly,  As  much  of  the  data  in  Table  XXI!  was  obtained  before  typical 
summer  weather  had  set  in.  it  Is  of  more  value  as  demonstrating  the 
relative  rate  of  oviposition  between  the  two  species. 

Tabi  i.  XXII.     Daily  rati  of  oviposition  of  A.  nubifera  and  A.  citri  compared. 


■ 

OP  I 

Da'' 
deposited. 

Dura- 
tion of 

laying. 

Number  of 

females 

of- 

Nomberof* a     Average  number 

D3                       laid 

Av«  : 

mean 

t.mpera- 
turr. 

Citri.     Nubifera. 

Citri.     Nubifera.     Citri.      Nubifera. 

1 

2... 

Apr.  20-21,1909 
Apr.  21-22, 1909 
do 

Hour*. 
23 
24 

24 
48 
48 
24 
24 

50                45 
40                44 

16 

36 

26 

30                79 
150 

454 

405 

345 
432 
200 
662 
516 
849 
1,558 

8 
10.1 
12.5 



9.9 

12                 10.8 
10. 4 

°F. 

80 

78 
80 

4 

5 

Apr.  22-24,1909 
Apr.  24-26,1909 
June  H^-17. 1909 
Julv  10-17.1907 

The  number  of  eggs  deposited  by  single  females  has  not  been 
definitely  determined.  However,  as  experiments  have  shown  that 
adults  of  A.  nubifera  are  capable  of  living  as  long  as  those  of  A.  citri 
and  have  been  known  to  maintain  unimpaired  an  average  of  about 
1  egg  per  day  less  than  A.  citri  for  at  least  seven  days,  it  is  safe  to 
say  that  the  maximum  egg  laying  capacity  is  not  far  from  200. 

When  all  food  plants  other  than  citrus  are  eliminated,  the  remarks 
covering  the  relation  between  oviposition  and  food  supply  for  A. 
citri  hold  for  A.  nubifera,  with  the  exception  thai  oviposition  with 
the  latter  species  is  far  more  dependent  upon  new  growth.  Tliis 
last  fact,  as  discussed  under  mortality  of  larvae  and  pupae  due  to 
overcrowding,  has  a  most  important  bearing  on  the  control  of  this 
species. 

After  a  grove  has  been  well  infested  with  the  cloudy-winged  wlute 
fly  there  exists  the  same  liigh  percentage  of  females  as  recorded 
under  the  same  topic  for  A.  citri.  In  fact,  the  same  proportion  of 
sexes,  and  the  same  fluctuations  and  dependence  of  sex  on  partheno- 
genesis, are  found  to  occur  with  A.  nubifera.  A  typical  example  is  the 
condition  found  in  one  grove  infested  entirely  by  this  species.  Dur- 
ing the  summer  preceding  winter  fumigation  the  ratio  between 
females  and  males  was  71.4:  28.6  pei  cent.    After  fumigation,  when 


100 


WHITE   FLIES   INJURIOUS   TO    CITRUS    IX    FLORIDA. 


over  99  per  cent  of  the  cloudy-winged  white  fly  were  killed,  the 
females  of  the  spring  brood  were  so  very  few  in  number  and  so  scat- 
tered that  they  deposited  a  very  large  percentage  of  infertile  eggs, 
resulting  in  a  second  brood  in  September,  62.8  per  cent  of  which  were 
males.  In  other  words,  after  the  natural  equilibrium  between  sexes 
had  been  disturbed  by  fumigation,  there  followed  as  the  result  of 
parthenogenesis  a  decided  fluctuation  between  a  predominance  of 
females  in  one  and  of  males  in  the  following  generations.  Gradually 
this  fluctuation  diminishes  until  normal  conditions  obtain. 

Wlule  less  attention  has  been  given  the  problems  connected  with 
the  emergence  of  tins  species,  observations  have  shown  that  the 
process  and  time  required  for  emergence  and  the  changes  in  color 
occurring  thereafter  are  the  same  as  for  the  citrus  white  fly,  with  the 
exception  of  the  cloud  at  the  tip  of  the  wing  already  mentioned. 
Statements  made  concerning  the  conditions  favorable  and  unfavor- 
able for  the  emergence  of  the  citrus  white  fly  hold  for  this  species. 
An  examination  of  the  extensive  daily  emergence  records  on  file  and 
summarized  in  Table  XXIII  show  that  even  during  October  and 
early  November  emergence  did  not  occur  below  an  average  daily 
mean  temperature  of  62°  F.  The  emergence  occurring  later  in  the 
fall,  and  consequently  during  cooler  weather,  does  not  appear  to  be 
due  to  more  resistance  to  cold,  but  to  a  difference  in  seasonal  history. 

Length  of  Life  Cycle. 

From  a  study  of  the  length  of  the  egg,  larval,  and  pupal  stages 
already  given  one  can  obtain  an  accurate  knowledge  of  the  length 
of  the  life  cycle.  A  general  summary  of  the  data  already  presented 
in  connection  with  these  various  stages  is  presented  in  Table  XXIII. 

Table  XXIII. — Length  of  life  cycle  of  cloudy -icing  ed  ichitefly  at  Orlando,  Fla. 


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egrees  accumulal 
before  spring  en 

genco. 

egrees  accumulal 
before       Last 
emerged. 

H 

Ph 

t-q 

- 

- 

A        -~ 

& 

- 

No  1 

Apr.  20 
June  16 

Aug.  23 

10 

51      334 

1,S00 

\"o  2 

Aug. 
Oct. 

2 
14 

47 
52 

1,849 
1,899 

No.  3.. 

Oct. 

31 

Mar.   20 

Mav    Hi 

266 

64.7 

35.  3 

5.205      7.062 

No.  4.. 

Sept.    4 

Oct. 

23 

Nov. 

1 

...do 

Apr.     1 

49     209 

73.2 

1 .  693 

4,706     5.0:5 

No.  5. . 

Sept.  IS 

Mar. 

22 

0 

Mar    22 

Mav      5 

185     229 

0 

100 

4.650 

4.650 

No.  6. . 

Sept.  21 

Mar. 

25 

0 

Mar.   2.3 

185     241 

0 

100 

4,638 

•      6.318 

No.  7.. 

Oct.      2 

Mar. 

18 

0 

Mar.   18 

167    

0 

100 

4.006 

4.006    

No.8.. 

...do 

Mar. 

an 

n 

Mar.   20 

169    

0 

100 

4.073 

4.C73    

No. 'J.. 

Oct.    22 

Mar. 

a 

0 

Mar.   21 

Apr.     9 

150     169 

0 

100 

3.549 

3,543     4.056 

It  will  be  noted  that  47,  the  least  number  of  days  required  for 
development,  is  but  slightly  higher  than  the  minimum  for  ^4.  c'drl, 
even  during  most  favorable  weather  conditions.     The  greater  average 


nil     (  i  mi  i>\    \\  i.m.i  D  WHIT]     PLY:  81  ISOH  \i.    3I8T0BY.        I'll 

Dumber  of  days  required  for  development,  shown  especially  l»\  com- 
parisons of  lots  i .  3,  »'».  and  7  of  Table  XXII]  and  lote  1 .  5,  I  I .  and 
15  of  Table  XV,  isnol  the  result  of  chance  circumstances,  but  actually 
the  result  of  slower  general  development  under  Identical  conditions. 
This  fact  is  perhaps  more  forcibly  brought  out  l>\  the  data  in  Table 
XXIV: 

Table   XXIV.     RaU  ofdt  velopment  of  A.  citri  and  .  I .  nubifera  compared. 


NTubl 

Date. 

[nstar 

Instar 

[nstar 

I  n>t  :ir 

[nstar 

l. 

-■ 

1. 

2. 

1. 

P.ct. 

P.  d. 

P.  a. 

July  6 

11.7 

58     ; 

0 

0 

22. 1 

0 

July  8 

2.1 

82.  7 

15.2 

0 

1.0 

0 

July  12 

.7 

L0.fi 

0 

1. 1 

67.8 

0 

Julv  16 

0 

1.8 

86.  1 

9.0 

0 

8.1 

91.1 

0.8 

July  21 

0 

20.6 

7'.  7 

0 

31.9 

Julv  25 

0 

0 

0.1 

93.9 

0 

July  29 

0 

0 

0 

100.0 

0 

0 

14.9 

<  >ctober  5 

Ms.  1 

1.6 

0 

.4 

0 

0 

October  n 

8.0  i 

0 

0 

0 
0 

92.0 
59.4 

2.4 
.9 
0 
0 

0 
40.0 
90.7 

17.2 

1.9 

1.9 

0 

0 

0 

0 

4.4 

80.3 

97.1 

98.  1 

36.  8 

1.8 

0 
0 
0 

64.2 

(8.8 

20.9 

3.3 

0 
0 

0 

1.1 

75.  1 
90.0 

12.7 

0 

i  1 .") 

0 

October  23 

0 

October  31 

1.8 

November  1 1 

71.8 

December  7 

December  17 

0 

0 

0 

100.0 

0 

0 

4.2 

December  26 

0 

0 

0 

100.0 

0 

0 

0 

100.0 

In  this  table  is  shown  the  corresponding  progress  of  growth  of 
both  species  on  various  dates  after  egg  deposition.  The  data  con- 
cerning development  during  July  refer  to  larvae  hatching  from 
laid  on  June  16,  1909,  and  that  during  October,  November,  and 
December  to  larvae  hatching  from  eggs  deposited  on  September  18, 
1909.  For  these  records,  leaves  on  the  same  shoot  were  chosen  for 
deposition  of  the  eggs  of  each  species;  hence  both  species  were  subject 
to  identical  climatic  and  nutritive  conditions. 

A  study  of  the  data  in  Tables  X  and  XXI  will  also  prove  that  the 
same  statements  made  for  A.  citri  concerning  the  equalizing  effect 
of  winter  on  the  length  of  the  pupal  stage  for  wintering-over  pupae 
are  equally  true  for  A.  nuhifera.  The  data  show  at  a  glance  that 
eggs  deposited  in  late  October  are  capable  of  producing  adults  the 
following  spring  as  early  or  even  earlier  than  eggs  deposited  a  month 
or,  as  sometimes  occurs,  five  months  earlier. 


SEASONAL    HISTORY. 

Generations  of  the  Cloudy-winged  "White  Fly. 

Aside  from  the  fact  that  the  adults  of  this  species  have  never  been 
seen  by  the  authors  on  wing  during  January  and  early  February,  as 
have  those  of  A.  citri,  there  being  therefore  no  winter  generation 


102  WHITE   FLIES   INJURIOUS    TO    CITRUS   IN    FLORIDA. 

corresponding  to  that  of  A.  citri,  the  statements  made  regarding  the 
number  of  annual  generations  of  A.  citri  is  true  of  A.  nubifera  when 
the  additional  statement  is  made  that  the  height  of  the  various 
emergence  periods  occurs  usually  about  two  or  four  weeks  later  than 
the  corresponding  periods  for  A.  citri.  The  emergence  of  adults 
brings  about  the  same  complications  in  broods  and  generations 
described  for  A.  citri,  resulting  from  variation  in  length  of  life  cycle, 
and  the  double-brooded  character  of  each  generation  is  also  to  be 
found  in  the  life  history  of  A.  nubifera.  Of  eggs  laid  August  23, 
1907,  1.5  per  cent  produced  adults  between  October  1  and  15  and  63.2 
per  cent  between  October  16  and  31 ;  of  the  remaining  pupae  wintering 
over,  34.6  per  cent  emerged  between  March  16  and  30  and  0.7  per  cent 
between  April  1  and  15.  From  eggs  laid  September  4,  1907,  24  per  cent 
of  the  adults  emerged  between  October  16  and  31,  2.8  per  cent  between 
November  1  and  15,  71.8  per  cent  between  March  16  and  30,  and  1.4  per 
cent  between  April  1  and  15.  From  eggs  laid  September  18, 1908,  81.6 
per  cent  of  the  adults  emerged  between  March  16  and  30,  4.1  per  cent 
between  April  1  and  15,  10.2  per  cent  between  April  16  and  30,  and 
4.1  per  cent  between  May  1  and  15.  From  eggs  deposited  March  29, 
1909,  44.5  per  cent  emerged  between  June  1  and  15,  no  further  records 
being  kept. 

It  might  be  inferred  from  the  slower  development  of  A.  nubifera 
that  it  would  pass  through  a  less  number  of  annual  generations  than 
A.  citri.  This,  however,  is  not  true,  inasmuch  as  its  slower  develop- 
ment is  offset  by  its  seasonal  history — it  remaining  active  later  in 
fall  and  early  winter. 

Seasonal  Fluctuations  in  the  Number  of  Adults  or  So-called  "Broods." 

Because  the  generations  of  the  cloudy-winged  white  fly  are  of  the 
same  general  double-brooded  character  as  those  of  the  citrus  white 
fly,  and  are  subject  to  the  same  unexplainable  variation  in  the 
length  of  the  life  cycle,  the  seasonal  history  of  A.  nubifera  is  not 
unlike  that  of  A.  citri  in  nearly  all  essential  features.  In  fact,  the 
same  three  periods  of  general  emergence  of  adults  occur  as  with  A. 
citri,  but  with  the  difference  that  the  adults  of  each  so-called  "brood" 
reach  their  numerical  maximum  usually  from  two  to  four  weeks 
later  than  the  corresponding  broods  of  A.  citri.  In  figure  19  are 
given  curves  representing  the  abundance  of  adults  of  A.  citri  and  A. 
nubifera  at  Orlando  during  1909.  As  a  result  of  this  striking  differ- 
ence in  the  seasonal  history  of  these  two  species,  previous  observa- 
tions on  this  subject  are  considerably  confused  and  should  be  disre- 
garded unless  one  is  positive  of  the  species  under  consideration  at  the 
time.  As  with  A.  citri,  no  one  definite  statement  can  be  made  to 
cover  the  exact  time  when  the  emergence  of  various  broods  will  begin. 
Emergence  is  strongly  influenced  by  local  weather  conditions.  While 
the  curve  in  figure  19  represents  the  condition  in  one  Orlando  grove 


Mil.    CLOUDS    WINGED    WHITE    I  I..  >NAL    IlISTOin 


L03 


in  L909j  it  Lb  not  meant  to  represent  the  abundance  of  adults  in  any 
<>t  ber  in  thai  city,  much  less  in  groves  in  various  parts  of  the 

State.  The  same  \  ariation  in  neighboring  ■/<  <»\  es  in  the  Bame  county 
and  in  a  lesser  degree  in  different  trees  in  the  same  grove  occurs  with 
A.  nubifera,  and  this  statement  apparently  holds  for  infested  gro 
in  ;ui\  pari  of  the  State.  For  example,  lti' > ^ « •  -  at  Dunedin  and 
Sutherland,  in  1909,  showed  a  difference  of  at  least  L0  days  in  the 
beginning  of  the  active  spring  emergence  of  adult-. 

The  most  striking  difference  in  the  seasonal  history  between  A. 
citr'i  and  A.  nubifera  which  perhaps  attracts  most  general  attention 
and  leads  to  more  confusion  between  the  two  species  in  the  mind-  of 

many  \s  the  nnieh  later  appearance  of  adults  of  A.  nubifera  in  the  fall 

of  the  year.  The  last  large  "  hatching"  of  A.  citri  is  on  a  rapid  decline 
at  Orlando  by  the  middle  of  September  at  the  latest,  while  that  of  A. 
nubifera  at  that  time  is  only  approaching  its  maximum  and  lasts  well 
toward  the   Nt   of  November,  when  its   decline   is    rapid,  although 

adults  can  be  found  during  moderately  warm  falls  as  Late  as  the  mid- 
dle of  December.      Thus  at  Orlando  in  October  18,  1907,  when  adult 


r£B#U*/fY 

/•r/wex 

*f>rrn. 

MAY 

JUM£ 

JULY 

AUGUST 

seprrrraex 

ocroeerm 

Novena&t 

oecs/»sc* 

/-/s 

/6-ee 

I-/S 

16-31 

/-/s 

/6-30 

,-,S 

/6-3/ 

/-/S 

/6-30 

/-/s 

/6-3/ 

/-/S 

AS -3/ 

/-/s\/e-3o 

/-'S 

/€-3f 

/-/s 

/6-30 

/-/s  /«-j/ 

i'ferc 

r 

--nu 

-=c/> 

r 

- 

-         >' 

•          . 

^^^ 

• 

V 

,.. 

— >^ 

: 

X 

■ 

"v 

_jy~~- 

^... 

__-''' 

"^ 

Fig.  19.— Diagram  showing  relative  abundance  of  the  adults  of  AUyrodes  nubifera  and  A.  citri, 
throughout  the  year  1909,  at  Orlando,  Fla.     (Original.) 

A.  citri  were  practically  off  the  wing  and  a  large  portion  of  the  imma- 
ture stages  of  A.  citri  had  already  reached  the  pupal  stage,  note  was 
made  that  adults  of  A.  nubifera  were  appearing  in  numbers  and  that 
pupae  of  A.  nubifera  were  rapidly  developing  eyespote  on  certain 
growths,  and  that  new  growth  in  places  was  crowded  with  ovipositing 
adults. 

In  consequence  of  the  difference  between  the  time  of  appearance 
of  these  fall  broods,  the  immature  stages  of  A.  citri  have  largely 
reached  the  pupal  stage  and  are  prepared  to  winter  over  by  the  last 
of  October.  At  this  time  females  of  .1.  nubifera  are  crowding  the 
limited  new  growth  with  large  numbers  of  eggs,  and  by  far  the  larger 
proportion  of  this  species  will  be  found  in  the  c^  and  larval  stages 
up  to  the  middle  of  December,  and  in  a  few  instances  third-instar 
larvae  may  be  found  as  late  as  the  middle  of  February.  It  will  be 
seen,  therefore,  from  this  and  the  foregoing  data  that  there  is  no 
time  during  the  season,  except  for  about  two  months  before  spring 
emergence  first  sets  in,  that  all  stages  can  not  be  found  in  the  grove 
in  varying  degrees  of  abundance. 


i  \  i)  i:  x 


I'.'IL'.'. 

Ailanthua glanduloaa,  reported  food  plant  <>i'  Aleyrodes eitri 

.1/,  urodothrips  fatciapi  tints,  enemy  of  Aleyrodes  citri 

AUyrodu  aurcmtii=  Aleyrodes  citri LO 

eitri 1 1  B5 

adult,  deecriptioD 

duration  of  life  v.  iih  and  withoul  food 71 

effect  of  wcai  her  conditions  on  activity 7^ 

emergence 67  71 

feeding  habits 

flighl  as  means  of  spread* 44-48 

mating 71  72 

ovipoeitioD 72  77 

an  orange  pest LO 

cheeks  on  successful  establishments 43  44 

distribution  in  foreign  countries 27-28 

United  States 25-27 

duration  of  adult  life 71 

egg,  description 53-58 

duration  of  stage 54-57 

hatching 57-58 

feeding  habits  of  adults 78-79 

larva*  and  pupae 65 

flight  of  adults  as  means  of  spread 44-48 

food  plants _ 

generations 81    s  \ 

growth 64 

historical  review 11-17 

history,  early,  in  United  States 12-14 

injury,  extent L9  26 

nature 17-19 

to  fruit 19-23 

trees 23 

killed  by  fungus  parasite  I  red  Aschersonia  l 39 

larval  stages,  descripl  ion 58-60 

duration 62 

feeding  habits 65 

growth 64 

locomotion 63 

molts (54-65 

life  cycle,  length. 80-81 

history  and  habits 51-86 

literature 1 4-17 

locomotion  ot  larval  stages 63 

losses,  summary 23-24 

mating 71-72 

105 


106  WHITE   FLIES   INJURIOUS   TO   CITRUS  IN   FLORIDA. 

Page. 

Aleyrodes  citri,  methods  of  study 52-53 

molts 64 

multiplication 79 

occurrence 10 

origin 11 

oviposition 72-77 

parthenogenesis 57 

proportion  of  sexes 77-78 

pupa  case,  description 61 

pupal  stage,  description 60-61 

duration 63 

feeding  habits 65 

restrictions  upon  multiplication  due  to  various  causes 79 

seasonal  fluctuations  in  the  numbers  of  adults  or  "broods" 84-85 

history 81-85 

sexes,  proportion ". 77-78 

spread  in  United  States 43-51 

summary  of  life  history  and  habits 51-52 

Jloccosa,  occurrence,  food  plants 10 

jloridensis ,  occurrence,  food  plants '. 10 

giffardi,  an  orange  pest 10 

occurrence,  food  plant 10 

howardi,  an  orange  pest 10 

discovery  in  Florida 11 

occurrence,  food  plant 10 

marlatti,  occurrence,  food  plant 10 

mori  arizonensis,  occurrence,  food  plant 10 

occurrence,  food  plant 10 

nubifera 86-103 

adult,  description  and  habits 98-100 

an  orange  pest 10 

'  distribution 89-90 

duration  of  instars 96-97 

egg 91-94 

feeding  habits  of  larvae  and  pupae 97 

food  plants 90 

generations 101-102 

growth 97 

habits  and  life  history 91-101 

history 86-87 

injury,  amount 87-89 

larval  and  pupal  stages 94-98 

stages,  description 94-95 

duration 96 

feeding  habits 97 

locomotion 97 

life  cycle,  length 100-101 

history  and  habits 91-101 

locomotion  of  larval  stages 97 

molts 97 

mortality  of  larvae  and  pupae 97-98 

occurrence,  food  plant 10 

pupa  case 95 


I  N  I » I  \.  ]()7 

AUyrodea  nub)fera1  pupa,  description 

pupal  stage,  duration 

Beasonal  fluctuations  in  number  of  adulta  or  '  broods"..     L02  LOS 

history i'»i   L08 

spread 90  91 

s/>iiii/( m,  occurrence,  food  plants i(> 

ttruthanthi,  occurrence,  food  plants lit 

vitriru Hub,  occurrence,  possible  food  planl 10 

Aleyrodide.    (Set  White  Hies.) 

Allamanda,  food  plant  of  M.  i/n></<s  citri 29,  13 

neriifolia.    (See  Ailamanda.) 
Alligator  pear,    i Set-  Persea  gratissima.) 

Aschersonia,  red,  fungus  parasite  oi  Aleyrodes  citri  in  tangerines :;u 

Ash.  green.    (See  Fraxvnus  IcmceolaCa.) 

prickly,  food  planl  of  Aleyrodes  citri 29,  12 

not  a  food  plant  of  Aleyrodes  nubift  m '.'<> 

Banana  shrub,  food  plant  of  Aleyrodes  citri •_"'.  13 

Bay.    I  See  Laurus  nobilis.) 

Hays.     (See  l\  rsea  spp.) 
Blackberry  (see  also  Rubus  spp.). 

food  plant  of  Aleyrodes  citri 29 

not  a  food  plant  of  Aleyrodes  nubift  ra 90 

Boats  as  means  of  spread  of  Aleyrodes  citri • 48-49 

( Jamellia,  food  plant  of  Aleyrodes  citri 30 

Gape  jessamine,  occurrence  of  Aleyrodes  citri  thereon 26 

Cherry  laurel,  food  plant  of  Aleyrodes  citri 29,  4.3 

not  a  food  plant  of  Aleyrodes  nubifera 90 

wild,  not  a  food  plant  of  Aleyrodes  nubifera 90 

China  tree,  food  plant  of  Aleyrodes  citri 29,  34-39 

not  a  food  plant  of  Aleyrodes  nubifera 90 

umbrella,  food  plant  of  Aleyrodes  citri 29,  34-39 

not  a  food  plant  of  Aleyrodes  nubifera 90 

Citrus  (see  also  Orange). 

food  plant  of  Aleyrodes  citri 29 

in  Florida,  injurious  white  flies 1-103 

nursery  stock  as  means  of  spread  of  Aleyrodes  citri 49-50 

relative  susceptibility  of  species  to  injury  by  Aleyrodes  citri 32-34 

trifoliata,  hedges,  occurrence  of  Aleyrodes  citri  thereon 26 

white  flies  that  breed  thereon  throughout  the  world 10 

fly.     (See  Aleyrodes  citri.) 
Coffea  arabica.     (See  Coffee.) 

Coffee,  food  plant  of  Aleyrodes  citri 29, 43 

Devilwood.     (See  Olive,  wild.) 
Diospyros  kaki.     (See  Persimmon,  Japanese.) 
virginiana.     (See  Persimmon,  wild.) 

Encarsia  variegata,  parasite  of  Paraleyrodes  persex 10 

Ficus  altissima,  reported  food  plant  of  Aleyrodes  citri 29 

carica,  cage  test  with  Aleyrodes  citri 30-31 

macropfajlla,  reported  food  plant  of  Aleyrodes  citri 29 

nitida,  food  plant  of  Aleyrodes  nubifera 90 

sp.,  reported  food  plant  of  Aleyrodes  citri  in  Costa  Rica 29 

Fig,  cultivated.     (See  Ficus  carica.) 

not  food  plant  of  Aleyrodes  nubifera 90 


108  WHITE    FLIES   INJURIOUS   TO    CITRUS   IK    FLORIDA. 

Page. 

Fraxinus  lanceolata,  food  plant  of  A  leyrodes  citrl 29 

Fungus  parasite.     (See  Aschersonia,  red.) 
Gardenia  jasminoides.     (See  Jessamine,  Cape.) 
Grapefruit.     (See  Citrus.) 

Grape,  not  food  plant  of  Aleyrodes  nubifera 90 

Gvmacum  officinale,  food  plant  of  Aleyrodes  fioccosa 10 

Gauva,  food  plant  of  Aleyrodes  floridensis 10 

not  food  plant  of  Aleyrodes  nubifera 90 

Gauvas 31 

Hedera  helix,  reported  food  plant  of  Aleyrodes  citri 29 

Honeysuckle,  food  plant  of  Aleyrodes  citri 29 

Humidity  as  affecting  emergence  of  Aleyrodes  citri 70-71 

Ivy,  English.     (See  Hedera  helix.) 

Jasminum  odoratissimum,  reported  food  plant  of  Aleyrodes  citri 29,  39-40 

Jessamine,  cape,  food  plant  of  Aleyrodes  citri 29,  39-40 

not  food  plant  of  Aleyrodes  nubifera 90 

yellow.     (See  Jasminum  odoratissimum.) 
King  of  Siam.     (See  Citrus.) 
Kumquat.     (See  Citrus.) 
Laurel  cherry.     (See  Prunus  caroliniana.) 

Laurus  nobilis,  reported  food  plant  of  Aleyrodes  citri 29 

Light  as  affecting  emergence  of  Aleyrodes  citri 71 

Ligustrum  spp.     (See  Privets.) 

Lilac,  food  plant  of  Aleyrodes  citri 29,  42 

Loranthus  (struthansus)  flexicaulis,  food  plant  of  Aleyrodes  struihanthi 10 

Magnolia,  cage  test  with  Aleyrodes  citri 30-31 

not  food  plant  of  Aleyrodes  nubifera 90 

fcetida.     (See  Magnolia.) 
fuscatum.     (See  Banana  shrub.) 

Man  as  agent  in  spread  of  Aleyrodes  citri 50-51 

Mandarin.     (See  Citrus.) 

Melia  azedarach.     (See  China  tree.) 

umbraculifera.     (See  China  tree,  umbrella.) 
Meliola.     (See  Sooty  mold.) 

camellix.     (See  Sooty  mold.) 

Michelia  flava,  food  plant  of  Aleyrodes  struthanthi 10 

Moms  spp 31 

Mulberries.     (See  Morus  spp.) 

Myrtle,  crape.     (See  Myrtus  lagerstrcemia.) 

Myrtus  lagerstrcemia,  cage  test  with  Aleyrodes  citri 30-31 

reported  food  plant  of  Aleyrodes  citri 29 

Oak  (see  also  Quercus). 

water,  reported  plant  food  of  Aleyrodes  citri 29 

Oaks 31 

not  food  plants  of  Aleyrodes  nubifera 90 

Oleander,  food  plant  of  Aleyrodes  citri 29 

Olive,  mock.     (See  Prunus  caroliniana.) 

wild,  food  plant  of  Aleyrodes  citri 29,  43 

Orange  (see  also  Citrus). 

reported  food  plant  of  Aleyrodes  vitrinellus 10 

Ornamental  plants  as  means  of  spread  of  Aleyrodes  citri 49-50 

Osmanthus  americanus.     (See  Olive,  wild.) 

Palmetto,  scrub,  food  plant  of  Aleyrodes  citri 29 


IN  hi  \.  1 09 

I*ur<tlt  i/mi/i a  /^  r  if  Encaraia  \  aru gata I') 

ii"!  likel)  to  be  Lnjuriou  i*» 

occurrence,  f 1  planl l') 

I *a  1-.1-1 1 . ■.  fungus,  enemj  of  Aleyrodea  citri.     (Se<  A.sch< 

Parthen me  is  as  affecting  proporl  ion  of  sexes  in  Ah  yrodea  citri 

in  .  lleyrodt  a  <'ifri 

Pear,  alligator.    (See  Peraea  gratiaaima.) 

cultivated,  food  plants  of  Aleyrodea  citri 

■  (/ratissiiun.  food  planl  of  Alt  ijm<h  s  jloridt  usi.s 10 

spp ' 31 

Persimmon,  Japanese,  food  plant  of  Aleyrodea  citri 29,41    12 

not  food  plant  of  .  l/<  yrodi  s  nubifi  ra !»<) 

wild,  food  plant  of  Aleyrodea  citri 29,41    12 

n- •!  food  plant  of  Aleyrodea  nubifera 90 

Pomegranate,  food  planl  of  Aleyrodea  citri 29,  13 

Prickly  ash.     (Set  Ash,  prickly.) 

Privets,  food  plants  of  Aleyrodea  citri 26,  29,  io   n 

not  food  plants  of  Aleyrodea  nubifi  ra 90 

Primus  caroliniana,  cage  teal  with  Aleyrodea  citri 30-31 

laurocerosu8.     (/See  Cherry  laurel.)  / 

PsiaHum  guajava.     (See  Guava.) 

spp.     (See  Guavas.  I 
Tunica  granatum.    {See  Pomegranate.) 
Pyrua  spp.     (See  Pear,  cultivated.) 
Quercus  (see  also  Oak). 

brevifolia,  cage  tost  with  Aleyrodes  eitri 30-31 

Railroad  trains  as  means  of  spread  of  Aleyrodes  citri ' 48    19 

Rearing  cages  for  j  1  leyrodes  citri 52-53 

Rosa  spp.,  food  plants  of  Aleyrodes  spinifera 10 

Rubber  tree.     (See  Ficus  nitida.) 

Rubus  spp.,  cage  tests  with  Aleyrodes  citri 30-31 

Satsuma.     (See  Citrus.) 

Smilax,  food  plant  of  Aleyrodes  citri 29, 43 

Sooty  mold  resulting  from  work  of  Aleyrodes  citri 17-19 

Syringasp.     (See  Lilac.) 
Tangerine.     (See  Citrus.) 

Temperature  as  affecting  emergence  of  Aleyrodes  citri 68-70 

Tree  of  Heaven.     (See  Ailanthus  glandulosa.) 
Umbrella  China  tree.     (See  China  tree,  umbrella.) 

Vehicles  as  means  of  spread  of  Aleyrodes  citri : 48-49 

Viburnum.     (See  Viburnum  nudum.) 

nudum,  food  plant  of  Aleyrodes  citri 29,  43 

Weather  as  affecting  activity  of  adults  of  Aleyrodes  citri 

White  fly,  citrus.     (See  Aleyrodes  citri.) 

cloudy-winged.     (See  Aleyrodes  nubi/era.  I 

investigations  in  Florida,  commencement 9 

woolly.     (See  Aleyrodus  howardi.) 

flies  injurious  to  Citrus  in  Florida 1-103 

species  affecting  Citrus  throughout  the  w >rld 10 

Winds  as  means  of  spread  of  Aleyrodes  citri 48 

Xanthoxylumclava-herculis.     (See  Ash,  prickly.) 

o 


UNIVERSITY  OF  FLORIDA 


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